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8551.

(a)Give any two examples for refraction of light in daily life. State the laws of refraction of light.b) "The power of a lens is -2.5D. Which type of lens is this?

Answer»

SOLUTION :(a)Lemon kept in water in a glass tumbler.
A pencil partly immersed in water in a glass tumbler.
Laws of refraction of light
i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane. ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant for the light of a given colour and for the given pair of media. This law is ALSO called as Snell.s law of refraction.
`(sin i )/(sin r) ` = constant
(b)A concave LENS has a NEGATIVE focal length. Hence it is a concave lens.
Discussion
8552.

Give an example of a metal which (i) is a liquid at room temperature. (ii) is kept immersed in kerosene for storing. (iii) is both malleable and ductile. (iv) is the best conductor of heat.

Answer»

Solution :(i) Mercury (HG) is liquid at room temperature :
(ii) Sodium (Na) is KEPT immersed in kerosene for storing.
(iii) Aluminium (AL) is malleable and ductile
(iv) SILVER (AG) is the best conductor of heat.
Discussion
8553.

(a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbons. (b) name the products formed when ethanol burns in air. List two forms of energy that are liberated on burning ethanol. (c). Why is the reaction between methane ad chlorine considered to be a substitution reaction?

Answer»

Solution :(a) Pass the vapours of given samples of the hydrocarbons into bromine water taken in two separate test tubes. The sample which discharge the colour of brominie water is that of unsaturated hydrocarbon while the one which does not discharge the colour of bromine water, represents saturated hydrocarbon.
(b) On burning ethanol in EXCESS of air, product is a mixture of carbon dioxide and water vapours. both heat and light are evolved in the combustion reaction.
`C_(2)H_(5)OH(l)+underset((Air))(3O_(2)(g))to2CO_(2)(g)+3H_(2)O(g)+heat+light`
(c) When methane is reacted with CHLORINE in the presence of sun light, tetrachloromethane is formed as the product. it is considered as substitution reaction because all the FOUR hydrogen atoms attached to carbon atom are REPLACED by chlorine atoms.
`underset("Methane")(CH_(4)(g))+4Cl_(2)(g)tounderset("Tetrachloromethane")(C Cl_(4)(g))+4HCl(g)`
Discussion
8554.

(i) Give a kherical test to distinguish between saturated and unsaturated hydrocarbons. (ii) Name the products fornted when ethanol burns in air. List two forms of energy that are liberated on burning ethanol. (iii) Why is the reaction between methane and chlorine considered a substitution reaction?

Answer»

Solution :a)Add bromise water .Saturated hydrocarbons do not react whereas unsaturated hydrocarbon will decolourise bromise water.
i) `CO_(2)` and `H_(2)O` are formed.
`C_(2)H_(5)OH(l)+3O_(2)(g)to2CO_(2)(g)+3H_(2)O(l)+Heat+light`
II)Heat energy and light energy.
c)It is because Cl atom SUBSTITUTES .H. atom of methane to from chloromthane and hydrogen CHLORIDE.
`underset("Metane")(CH_(4)(g)+)underset("Clorine")(Cl_(2)(g))overset(sunlight)tounderset("Chloromehane")(CH_(3)CL(g)+Hel(g))`
Discussion
8555.

A gaseous hydrocarbon gives upon combustion 0.72g of water and 3.08g of CO_(2). The empiricalformula of the hydrocarbon is

Answer»

`C_(6)H_(5)`
`C_(7)H_(8)`
`C_(2)H_(4)`
`C_(3)H_(4)`

ANSWER :B
Discussion
8556.

A gas is produced when conc. H_2SO_4 is added to solid sodium chloride taken in a test tube. The gas coming out of the delivery tube is passed over a dry blue litmus paper and then over a moist blue litmus paper. What would you observe ? Explain reason with the help of a chemical equation.

Answer»

Solution :HCl gas is produced when conc. `H_2SO_4`is added to solid sodium chloride.
`NaCl + H_2SO_4 toNaHSO_4 + HCl`
HCl gas when passed over dry blue litmus paper shows no effect.
HCl gas when passed over MOIST blue litmus paper TURNS it RED.
This is because dry HCl gas does not produce `H^+`ions, therefore there is no action on dry blue litmus paper. Moist blue litmus paper contains water. HCl gas when passed over moist blue litmus paper reacts with water to FORM `H^+` ions. An acid (containing `H^+`ions) turns blue litmus red. Therefore,a red colour will be obtained.
Discussion
8557.

A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer»

SOLUTION :Gas EVOLVED is hydrogen.
`2CH_(3)CH_(2)OH+2Na to 2CH_(3)CH_(2)O^(-)Na^(+)+H_(2)`
Discussion
8558.

A gas is evolved when sodium carbonate reacts with propanoic acid. Write the balanced chemical equation between the two given reactants. Show the acidic nature of propanoic acid by any two methods.

Answer»

Solution :`2CH_3CH_2overset(O)overset(||)(C )-OH+ Na_2CO_3 to 2CH_3CH_2overset(O)overset(||)(C )-O^(-)Na^(+) + H_2O + CO_2`
The other tests that can be used to check ACIDITY of propanoic acid are:
a) Litmus test: propanoic acid turns blue litmus red.
b] Reaction with sodiuin: When propanoic acid reacts with a HIGHLY reactive metal like sodium, it undergoes displacement reaction, releasing hydrogen.
`CH_3CH_2overset(O)overset(||)(C ) -OH+Na to CH_3CH_2overset(O)overset(||)(C )-O^(-)Na^(+) + 1//2H_2`.
c]Reaction with a base: When propanoic acid reacts with an alkali like sodium hydroxide, it undergoes neutralization reaction, FORMING sodium propanoate and water.
Discussion
8559.

A gas cylinder is filled with helium at 2000 mm. Due to leakage, thepressure dropped to 1500 torr in 40 min. When thesame cylinder is filled with another gas at the same pressure, the pressure dropped from 2000 mmto 1500 mm in 200 min. What is themolecular weight of thegas?

Answer»

SOLUTION :(i) relation between DROP in pressure and rate ofdiffusion
(ii) relation between the rate of DIFFUSION andmolecular WEIGHT of gases
(iii) 100
Discussion
8560.

(a) From the following group of organisms create a food chain which is the most advantageous for Human beings in terms of energy. (b) State the possible disadvantage if the cereal plant is growing in soil rich in pesticides. (c ) Construct a food web using the organisms mentioned above.

Answer»

SOLUTION :(a) Cereal plant `to` Goat `to` Human being
Since this has LEASTNUMBER of trophic levels, so it most beneficial to Human BEINGS in terms of energy.
(b) Biggest disadvantage of using PESTICIDES in the soil used for growing cereal crops is that these chemicals will reach in maximum in our BODIES due to the phenomenon of Biological Magnification.
(c )
Discussion
8561.

A fresh piece of Mg ribbon loses its luster after a few days. This is due to the formation of the compound………………

Answer»


ANSWER :MGO
Discussion
8562.

(a) For the combination of resistors shown in the following figure, find the equivalent resistance between M and N. (b) State Joule.s law of heating. (c ) Why are need a 5A fuse for an electric iron which consumes 1 kW power at 220 V? (d) Why is it impracticable to connect an electric bulb and an electric heaterin series?

Answer»

Solution :(a) We have `R_(1) and R_(2)` is series with the parallel combination of `R_(3) and R_(4)`. Hence, equivalent resistance between M and N is :
`R=R_(1)+R_(2)+(R_(3)R_(4))/((R_(3)+R_(4)))`
(b) When a current I is PASSED through a resistor R for a time t, the amount of heat produced .H. is given by the RELATION
`H=I^(2)Rt`
This is known as Joule.s law.
(c ) For an electric iron consuming 1 kW electric power at 220 V, current FLOWING through the element.
`I=(P)/(V)=(1kW)/(220V)=4.54A`
Therefore, we use a fuse of 5 A current rating.
(d) In a series circuit same current flows throughout the electric circuit. Thus, it is impracticable to connect an electric bulb and an electric heater in series because they need CURRENTS of widely different values to operate properly.
Discussion
8563.

A food chain in a polluted aquatic ecosystem is given. Observe it and answer the following questions. Fresh water to Algae to Fishes to Birds. (i) Which organisms are disturbed more due to biomagnification? Why? (ii) This ecosystem will be destroyed gradually due to biomagnification. Why?

Answer»

SOLUTION :(i) Birds are disturbed more due to biomagnification.
As the birds occupy the top most levl in the given food chain, the maximum concentration of harmful CHEMICALS causing biomagnification get ACCUMULATED in their body.
(ii) Biomagnification is the process of ACCUMULATION of nondegradable chemicals in the various trophic levels of food chains.
As the chemicals are non-degradable or cannot be washed, they cannot be removed from the organisms of the food chain. This leads to gradual destroying of the ecosystem.
Discussion
8564.

A flask P contains 0.5 mole of oxygen gas. Another flask Q contains 0.4 mole of ozone gas. Which of the two flask contains greater number of oxygen atoms?

Answer»

<P>

Solution :`"1 MOLECULE of oxygen "(O_(2))="2 atoms of oxygen"`
`"1 molecule of ozone "(O_(3))="3 atoms of oxygen"`
`"In FLASK P : 1 mole of oxygen gas"=6.022xx10^(23)" molecules"`
`+"0.5 mole of oxygen gas "=6.022xx10^(23)xx"0.4 molecules"`
`=6.022xx10^(23)xx0.4xx"3 atoms"=7.23xx10^(22)" atoms"`
`therefore` Q has a greater number of oxygen atoms as compared to the flask P.
Discussion
8565.

A few crystals of copper sulphate are heated in B/F dry boiling tube: (i) What is the colour before and after heating? (ii) What is the reason for the colour change? (iii) Can its original colour be restored? How?

Answer»

Solution :(i) Blue and white RESPECTIVELY
(II) Water of crystalization is lost on heating.
(III) YES by adding water
Discussion
8566.

Stars appear to be twinkling but planets do not twinkle. Why? Explain why the colour of the clear sky during day appears blue and during sunset appears red.

Answer»

Solution :Planets are much closer to the earth and are seen as exended SOURCES, so a PLANET may be considered as a collection of a large number of point size light sources, although light comingfrom individual point sized sources flicks but the total amount of iight entering our eye from all the individual point sized sources average out to be constant thereby plancts appear equally bright and there is no TWINKLING of planets.
Clear sky appears blue when sunlight passes through the atmosphere having the molecules of air and other fine particles whose size is smaller then the wavelength of visible light. These molecules and perticular SCATTER the bluc colour nmore strongly then the other colours of spectrum. As the walength of blu: colour is more, this scaltered blue light enters our eye, so, the colour of sky appcars blue to us during day TIME.
Discussion
8567.

a)Explain why variations are observed in the offsprings formed by sexual reproduction? b) What are the advantages of vegetative propagation?

Answer»

Solution :a)During sexual reproduction two different parent i.e, male and female take part as a result of which the newly formed zygote possess genetic material of both PARENTS. It leads to interchange of genetic INFORMATION between two gamete which is passed to the progeny and develops variation. Offspring produced as a result of sexual reproduction are genetically different from the parents due to the process of meiosis, during which crossing over takes place which creates recombination.
b)Advantages of vegetative propagation:
* It is USED to grow a plant in which viable seeds are not formed or very few seeds are produced such as orange, banana, pineapple.
* It helps to introduce plants in new areas where the seed germination fails to produce mature plant due to change in environmental factors and the soil.
* It is more rapid, casier and CHEAPER method.
*By this method a good quality of a race or VARIETY can be preserved.
Discussion
8568.

Explain the terms (i) Speciation(ii) Natural selection

Answer»

Solution :a) i) Speciation : Speciation is the evolution of reproduction isolation among once interbreeding POPULATION i.e, the development of one or more species from an existing species.
ii) Natural selection : Natural relationship in the process, ACCORDING to Darwin, which bring about the evolution of new species of animals and parents.
b) Four factors which can lead to speciation are :
GENETIC drift : Over generation, genetic drift may accumulate which lead to speciation.
Natural selection : Natural selection which may GIVE rise to speciation.
Severe DNA CHANGE
A variation may occur which does not allow sexual act between two groups.
Discussion
8569.

(i) Write the electron dot structure for sodium, oxygen and magnesium. (ii) Show the formation of Na_(2)O and MgO by the transfer of electrons. (iii) What are the ions present in these compounds.

Answer»

Solution :a) Sodium has one electron in the outermost shell while OXYGEN has six. To complete its octet. Oxygen needs TWO more electrons. But to complete the octet, sodium LOSES one electron. In order to EQUALISE the number of electrons lost and gained, two atoms of sodium combine with one atom of oxygen. The formation of `Na_2O`is shown below

b) BRONZE is made up of copper and tin.
Discussion
8570.

An electric bulb is connected to a 220 V generator. The current is 0.5 A. What is the power of the bulb ?

Answer»

Solution :(a)The heating effect of electric current is used in the following applications.
Electric bulb : In an electric bulb, the filament of bulb gives light because of heating effect of electricity. The filament of bulb is generally MADE of tungsten METAL, having melting point equal to `3380^@C.`
Electric iron : The element of electric iron is made of alloys having high melting point. Electric heater and GEYSER work on the same mechanism.
Given V = 220 , I = 0.5 A, P = ?
P = VI
` = 220 V xx 0.50A `
= 110 J/S
= 110 W
Discussion
8571.

A dry pellet of a common base B, when kept in open absrobs moisture and turns stickly. The compound is also a by-product of chlorialkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide ? Write a balanced chemical equation for one such solution.

Answer»

Solution :Sodium hydroxide (NaOH) is a commonly used BASE and is hygroscopic, that is it absorbs moisture from the atmosphere and becomes stickly.
The acidic oxides reacts with base to GIVE salt and water. The reaction between NaOH and `CO_(2)` can be GIVEN as
`2NaOH + CO_(2) RARR Na_(2)CO_(3) + H_(2)O`
Discussion
8572.

A dry pellet of a common base B , when kept in open absorbs moisture and turns sticky. The compound is also a by - product of chlor - alkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.

Answer»

Solution :Sodium hydroxide (NaOH) is a COMMONLY used base and is hygroscopic , that is , it ABSORBS moisture from the atmosphere and becomes sticky.
The acidic oxides REACT with base to give salt and water. The REACTION between NaOH and `CO_2` can be given as
`2NaOH + CO_(2) rarr Na_(2)CO_(3) +H_(2)O`
Discussion
8573.

A drop of colourless liquid was placed on blue litmus paper. The litmus paper turned red. The liquid could be:

Answer»

dilute HCI
dilute NaOH SOLUTION
DISTILLED WATER
`NaHCO_(3)` solution

ANSWER :A
Discussion
8574.

(a) Draw a diagram showing germination of pollen on stigma of a flower and mark on it the following organs/parts: (i) Pollen Grain (ii) Pollen tube (iii) Stigma (iv) Female germ cell (b) State the significance of pollen tube. (c ) Name the parts of flower that develop after fertilisation into (i) Seed (ii) Fruit

Answer»

Solution :(a)
(b) Process of fertilisation:
(i) On reaching the stigma, pollen grain germinates, CARRYING the two male gametes in pollen tube.
(ii) The first male gamete fuses with the egg cell, PRESENT in the embryo sac resulting in formation of zygote.
(iii) The second male gamete fuses with secondary NUCLEI and result in formation of primary ENDOSPERM nucleus. This is known as DOUBLE fertilisation.
(iv) After fertilisation, the ovule develops and converts into a seed containing embryo. The embryo is the future plant and when it is provided with suitable conditions like water, air and optimum temperature, it develops into a seedling.
(c ) (i) The ovary grows rapidly and ripens to form a fruit. The fruit encloses the seeds. The seed contains embryo which has a plumule and a radicle. Radicle gives rise to root and plumule gives rise to shoot.
(ii) Ovule forms the embryonal axis inside the seed.
Discussion
8575.

A double bond between two carbon atoms is formed by

Answer»

the transfer of two electrons from ONE CARBON atom to the other
the transfer of one electronfrom one carbon atom to the other
two shared ELECTRON PAIRS
the sharing of two electrons

Answer :C
Discussion
8576.

(a) Distinguish between 'roasting' and 'calcination'. Which of the two is used for sulphide ores and why ? (b) Write a chemical equation to illustrate the use of aluminium for joining craked railway lines. (c ) Name the anode, the cathode and the electrolyte used in the electrolytic refining of impure copper.

Answer»

Solution :(a) For distinction between CALCINATION and roasting.
For the sulphide ores, the process of roasting is commonly used. It is carried by heating the ore helow its melting point with excess of air. As a result, the sulphide ore is converted to its oxide form. For example,
`underset(("Zinc blende"))(2ZnS)+ 3O_(2)rarr2ZnO + 2SO_(2)(g)`
`underset(("Galena"))(2PbS) + 3O_(2) rarr2PbO + 2SO_(2)(g)`
(b) Cracked railway lines can be joined or welded with the help of thermit welding. Thermit is a mixture of ferric oxide and aluminium powder. The chemical equation involved is :
`2Al + Fe_(2)O_(3) rarr Al_(2)O_(3) + underset(("Molten"))(2Fe) + "heat (exothermic)"`
For the details of the process.
(c ) In the electrolytic refining of copper ,
ANODE : A rod of impure copper.
Cathode : A rod of pure copper.
Electrolyte : An aqueous solution of copper sulphate CONTAINING a small amount of sulphuric ACID.
Discussion
8577.

(a) Distingusihbetweenesterficationand saponificationreactions with the help of chemicalequations for each. (b) Witha labelled digaram describlein brief an acitivityto showthe formation of an ester.

Answer»

Solution :(a) In the esterification reactino an acid reacts with alcohol in the presence of conc. `H_(2)SO_(4)` to form an ester with a leasant or fruity SMELL. For example,
`underset("Ethanoic acid")(CH_(3)COOH)+underset("ETHANOL")(C_(2)H_(5)OH)OVERSET(H_(2)SO_(4)(conc.))tounderset("ETHYL ethanoate (ester)")(CH_(3)COOC_(2)H_(5))+H_(2)O`
Saponification is quite different from esterification because in this case an ester reacts with an ALKALI
(NaOH or KOH) to form salt of acid and alcohol. for example.
`underset("Ethyl ethanoate")(CH_(3)COOC_(2)H_(5))+NaOHtounderset("Sod. ethanoate")(CH_(3)COONa)+underset("Ethanol")(C_(2)H_(5)OH)`
(b).
Discussion
8578.

A displacement reactionin whichthe acidreactswith thebaseto forma saltand wateris called _____ reaction .

Answer»

SOLUTION :NEUTRALIZATION
Discussion
8579.

a) Discuss any two achievements of the Modern Periodic Table. b) Discuss any two limitations of Mendeleev's classification. c) How were these removed in the Modern Periodic Table?

Answer»

SOLUTION :a) Two achievements of Modern Periodic Table are:
i] It is based on the atomic number which increasesuniformly by one from element to element. Hence, it is more accurate.
ii] All elements having similar properties are placed in the same group. It has accommodated all the known elements TILL date.
b] Two limitations of Mendeleev.s classification:
i] Isotopes discovered several years later posed a challenge to Mendeleev.s table. These had different atomic masses but same chemical properties and hence, did not obey periodic law. They could neither be placed in the same group (since they had different atomic masses) nor in different groups (since their properties were same). Thus, their position in the Periodic Table could not be decided properly.
ii] Like alkali metals, hydrogen combines with HALOGENS, OXYGEN, and sulphur to form compounds having similar formulae (for example: HCI, H2O, H2S which can be compared with NACL, Na2O and Na2S respectively). On the other hand, like halogens, hydrogen exists as a diatomic molecule and combines with metals and non-metals to form covalent compounds. Hence, Mendeléey could not give a fixed position to hydrogen in his Periodic Table.
c] i]In Mendeléey.s Periodic Table, hydrogen could notbe allotted a fixed position since it showed properties similar to both alkali metals and halogens. In the Modern Periodic Table, this anomaly is resolved by placing hydrogen in the top left corner separately since it has special properties that are not found in any other element.
ii] In Mendeléey.s Periodic Table, isotopes of an element (same chemical properties) could not be placed in the same position since they have different atomic masses. But in the Modern Periodic Table, isotopes (same atomic number) can be placed in the same position.
Discussion
8580.

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified potassium permanganate solution. The light purple colour of the solution fades and finally disappears. Write the correct explanation for this observation.

Answer»

Solution :Potassium PERMANGANATE solution `(KMnO_(4))` is an OXIDISING agent. It oxidises ferrous sulphate `(FeSO_(4))` to FERRIC sulphate `[Fe_(2)(SO_(4))_(3)]`.
Discussion
8581.

A dilute ferrous sulphate solution was added to the beaker containing acidified permanganate solution. The light - purple colour of the solution fedes and then disappears. Which of the following of the correct explanation for the observation ?

Answer»

PERMANGANATE is an OXIDIZING agent and it oxidizes sulphate.
Ferrous sulphate is an oxidizing agent and it oxidizes permanganate.
The colour DISAPPEARS DUE to DILUTION, no reaction is involved.
Permanganate is an unstable compound and undergoes decomposition in the presence of ferrous sulphate to a coloured compound.

Answer :A
Discussion
8582.

(a) Did Debereiner's triads also exist in the columns of Newland's law of octaves? Explain your answer. (b) What were the limitaions of Debereiner's classification of elements? (c) What were the limitations of Newlands' lawof octaves?

Answer»


SOLUTION :NA
Discussion
8583.

A diagram of traditional water harvesting system is given below: The statement which defines the system and its parts is

Answer»

This is an idealsetting of the KHADIN system and A = CATCHMENT area, B = Saline area and C = Shallow dugwell.
This is an ideal setting of the Shallow dugwell system and A = Catchment area, B = Saline area and C = Khadin.
This is an ideal setting of Catchement area and A = Khadin, B = Saline area and C= Shallow dugwell.
This is showing Saline area and A = Catchment area, B = Khadin and C = Shallow dugwell.

SOLUTION :This is an idealsetting of the Khadin system and A = Catchment area, B = Saline area and C = Shallow dugwell.
Discussion
8584.

(a) Describe an activity with diageam to illustrate that the reaction of metal carbonates or metal hydrogen carbonates with acids produces carbon dioxide. Write the relevant equations of all the reactions that take place. (b) Name any two forms in which calcium carbonate is found in nature.

Answer»

Solution :(a) Take a SMALL amount of metal carbonate such as `(Na_(2)CO_(3))` or metal hydrogen carbonate `(NaHCO_(3))`and to this add few drops of dilute hydrochloric acid. The reaction immediately starts resulting in the evolution of carbon dioxide GAS which is evolved with brisk effervesscence. With th help of a delivery tube, pass the vapours of the gas evolved into LIME water. Calcium hydroxide present in lime water immediately becomes milky due ot formation of solid calcium carbonate. The chemical reactions that occur are listed as follows :
`Na_(2)CO_(3)(s)+2HCl(AQ)to2NaCl(aq)+H_(2)O(aq)+CO_(2)(g)`
`NaHCO_(3)(s)+HCl(aq)to NaCl(aq)+H_(2)O(aq)+CO_(2)(g)`
`underset(("Lime water"))(Ca(OH)_(2)(aq))+CO _(2)(g)tounderset(("White ppt."))(CaCO_(3))(darr)+H_(2)O(aq)`
Calcium carbonate `(CaCO_(3))` occurs as marble and also as lime stone.
Discussion
8585.

(a) Describe an activity to show that metals are good conductors of electricity.(b) Account for the following:(i) Hydrogen gas is not evolved when a metal reacts with nitric acid. (ii) For storing sodium metal, it is kept immersed in kerosene. (iii) The reaction of iron (III) oxide with aluminium is used to join cracked iron part machines.

Answer»

Solution :
(a) Activity:
(1) Set up an electric circuit as shown in the figure.
(2) Place the metal to be tested in the circuit between terminals A and B as shown.
(3) We find that the bulb glows. This shows that metals aregood conductors of electricity.
(b) (i) This is because the hydrogen gas first evolved reacts with `HNO_3`to produce oxides of nitrogen.
(ii) We cannot store it under WATER because sodium reacts with water to produce hydrogen gas.
`2NA + 2H_2O to 2NaOH + H_2`
(iii) `FeO_3 + 2AL to Al_2O_3 + 2Fe` + heat
This is EXOTHERMIC REACTION. The molten iron is used to join cracked iron parts of machine.
Discussion
8586.

(a) Define the following terms: (i) Valency, (ii) Atomic size. (b) How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table ?

Answer»

SOLUTION :(a) (i) Valency : The combining POWER or the combining capacity of an atom is called its valency.
(ii) Atomic size: Atomic size or atomic radius is the distance between the centre of the nucleus and the outermost shell of an ISOLATED atom.
(b) On moving from left to right in the periodic table, valency increases up to 4 and then decreases. The ELECTRONS present in the last shell determine the valency of a particular element.
If the number of valence electrons is less than or equal to 4, valency = number of valence electrons If the number of valence electrons is more than 4, valency = 8 - number of valence electrons
Atomic size decreases along a period. This is because on moving across a period, the number of valence shells remains the same and the electrons increase by one unit. As a result, the nuclear charge increases and thus, the atomic radius decreases.
Discussion
8587.

a) Define speciation? b) Mention the sex chromosomes present in human male and human female with the help of a flow chart determine genetically in human beings the sex of the offspring if the sperm carrying x chromosomes fertilizers the egg.

Answer»

SOLUTION :a) Speciation is arising of a new species from a sub-population of a species which is geographically or REPRODUCTIVELY ISOLATED over a long PERIOD of time from the other population of the same species.
b)
Discussion
8588.

a) Define evalution? Describe the contribution of landmark. b) How do homologous organs provide evidence in support of evolution ?

Answer»

Solution :a) Evalution is referred to as the changes acqired by a species or a certain population of a species gradully over a long period of time these changes should he heritable contribution of landmark According to the theory of inheritance of acquired CHARACTERS or Lamarkism. put forward by lamark. The use and disuse or an organ leads to acquiring change in the FEATURE of that organ these change are also inherited by the offsprings the favorable variations caused due to use and DISUE after a considerably long period of time result in evolution of a new species.
b) The presence of homologous organs indicates that all vertebrates have a common ANCESTRY. Similarly all organs and system of the vertebrates show the fundamental similarities which point TOWARDS common ancestry.
Discussion
8589.

(a) Define corrosion, what is the nature given to corrosion of iron ? (b) Name the colour of coating formed on silver and copper when exposed to air. (c ) List two damages caused by corrosion and suggest, how these can be prevented.

Answer»

Solution :(a) For definition of corrosion. Corrosion of iron is known as rusting.
(b) COATING DEPOSITED on the surface of silver metal is of silver sulphide `(Ag_(2)S)`. It is black in COLOUR. The coating deposited on copper surface is of basic copper carbonate `Cu(OH)_(2)CuCO_(3)`. It is GREEN in colour.
Discussion
8590.

a) Define electric power express it in terms of potential difference V and resistance R. b) What is meant by saying that the potential difference between two points is 1V?

Answer»

<P>

Solution :a) Electric power : it is the rate of doing work by an energy source or the rate at which the electrical energy is dissipated or consumed per unit time in the electric ciruit is called electric power.
so, `"Power P"= ("work done (W)")/("time(t)")`
`=("Electrical energy dissipated")/("Time(t)")=VI = V^(2)R`
b) If 1 I of work is reqired to MOVE a charge of amout IC from one point to another then it is SAID that the potential difference between the two points is1V.
Discussion
8591.

(a) Define allotropy. (b) Name three allotropic forms of carbon.

Answer»

SOLUTION :Allotropy . When an element EXISTS in more than one form having different physical properties but same or slightly different chemical properties, the various forms are called ALLOTROPIC forms or allotropes and this PHENOMENON is called allotropy.
The element like cabon, sulphur , PHOSPHORUS etc, show allotropy.
The three allotropic forms of carbons are :
(i) Diamond (ii) Graphite (iii) Fullernens.
Discussion
8592.

a) Define 1 dioptre of power of a lens b) The refractive index of diamond is 2.42. What is the meaning of this statement. c) In which type of lens linear magnification is always less than one ?

Answer»

Solution :a) The SI unit of POWER of lens is dioptre which is denoted by the letter D. 1 Dioptre is defined as the power of a lens of FOCAL length 1 meter.
b) The refractive index of diamond is 2.42 this means that the speed of light in diamond will reduce by a factor of 2.42 as compared to its speed in AIR. In other words the speed of light in diamond is 2.42 times less than the normal speed of light in vacuum.
c) Concave lens always has linear magnification less than ONE, because it always gives diminished images.
Discussion
8593.

A dam is constructed to prevent _____ in rivers.

Answer»


ANSWER :FLOODS
Discussion
8594.

A dam is built with a view to

Answer»

make water AVAILABLE for drinking
increase SARDINE catch
check overflow of rainwater

Answer :C
Discussion
8595.

A cylindrical conductor of length .l. and uniform area of cross section.A. has resistance .R.. The area of cross section of another conductor of same material and same resistance but of length .2l. is

Answer»

`(A)/(2)`
`(3A)/(2)`
2A
3A

Solution :Here `R=(RHO l)/(A)=(rho(2L))/(A.) RARR A.=2A`
Discussion
8596.

A cyclic compound 'X' has the molecular formula CH. It is an unsaturated compound and burns with a sooty flame. Identify 'X' and write its structural formula. Is 'X' more reactive than its saturated homologue and if so, why?

Answer»

SOLUTION : .X. is benzene. Structural FORMULA of benzene is

Benzene is more REACTIVE than its saturated homologue as the DOUBLE bonds INCREASE the reactivity.
Discussion
8597.

A cyclic compound 'X' has molecular formula C_(6)H_(6). It is an unsaturated compound and burns with sooty flame. Identify 'X' and write its structural formula.

Answer»

Solution :`X="BENZENE"//C_(6)H_(6)`
STRUCTURE
Discussion
8598.

A current of 9.65 A is passed through three different electrolytes NaCl, AgNO_(3) and CuSO_(4) for 30 min separately. Calculate the ratio of the metals deposited at the respective electrodes. Also find out the weights of various metals deposited at the respective electrodes

Answer»

Solution :Quantity of electricity passed through the electrolyte = current strength `xx` time of flow = `9.65 xx 30 xx 60` coulombs
`m_(Na) : m_(AG) : m_(Cu) = E_(Na) : E_(Ag) : E_(Cu)`
`E_(Na) = (23)/(1) = 23 "" (Na^(+) + E^(-) rarr Na)`
`E_(Ag) = (108)/(1) = 108 (Ag^(+) + e^(-) rarr Ag)`
`E_(Cu) = (63.5)/(2) 31.75 "" (Cu^(+2) + 2e^(-) rarr Cu)`
`m_(Na) : m_(Ag) : m_(Cu) = 23 : 108 : 31.75`
Weight of sodium deposited `= (23 xx 9.65 xx 30 xx 60)/(96500) = 4.14g`
Weight of silver deposite `= (108 xx 9.65 xx 30 xx 60)/(96500) = 19.44 G`
Weight of copper deposited `= (31.75 xx 9.65 xx 30 xx 60)/(96500) = 5.715g`
Discussion
8599.

A current 5.00 A liberates 0.252 g of hydrogen in certain time. How many grams of oxygen, aluminium and sodium can be liberated or deposited by the same current in the same time ?

Answer»

Solution :(i) The number of gram EQUIVALENTS is same when the same amount of charge is passed through.
(ii) Calculation of total charge required to produce 0.252 g of hydrogen.
(III) Calculation of the amounts of other products BASED on the quantity of charge passed through the RESPECTIVE ELECTROLYTES.
Discussion
8600.

(a) Crystals of a substance their colour on heating in a closed test tube but regained it after sometime when they were allowed to cool down. Name the substance and write its formula and explain the phenomenon involved. (b) name the acid and base that would be used to prepare the following salts: (i) Potassium sulphate (ii) Ammonium chloride.

Answer»

Solution :(a) COPPER sulphate crystals `(CuSO_4. 5 H_2O)`
5 molecules of water are present in ONE formula unit of copper sulphate. When heated, it loses its water and salt turns white.
(b) BASIC Salt:
(i) Base: KOH (Potassium HYDROXIDE)
Acid: `H_2SO_4` (Sulphuric acid)
(ii) Base: `NH_4OH` (Ammonium hydroxide)
Acid: HCl (HYdrochloric acid)
Discussion