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2351.

When a metal X is treated with cold water, it gives a basic salt Y with molecular formula XOH (Molecular mass=40) and liberates a gas Z which easily catches fire. Identify X,Y and Z and also write the reaction involved.

Answer»

Solution :Sodium (Na) and potassium (K) react with COLD WATER to form basic SALT. NaOH and KOH respectively . The MOLECULAR mass of NaOH is 40. So, X is Na and Y is NaOH. The gas liberated during the REACTION is hydrogen `(H_2)`. So Z is `H_2`
`2Na+2H_2 O to 2NaOH+H_2+ Heat energy`
Discussion
2352.

What are periodic properties?

Answer»

SOLUTION :The PROPERTIES which SHOW gradual variation in agroup and in a period and they repeat themselvesafter a certain INTERVAL of atomic number arecalled periodic properties.
Discussion
2353.

Which of the following molecule has largest bond angle?

Answer»

`H_(2)O`
`NH_(3)`
`CO_(2)`
`CH_(4)`

Answer :c
Discussion
2354.

what is slag ? Give example

Answer»

Solution :SLAG is a fusibel product formed when flux REACTS with gangue during the extraction of metals .
Flux + gangue `rightarrow` slag
`CaO + SiO_(2)rightarrowCaSiO_(3)`
Discussion
2355.

There are three elements X, Y and Z having atomic numbers of 6, 16 and 19 respectively. Based on this information, Het has been asked to answer the following questions: What will be the formula of covalent compound formed ?

Answer»

SOLUTION :In order to answer these questions, Het first wrote down the electronic configurations of the elements X, Y and Z by USING their atomic numbers, as follows:

(5) The element X has 4 valence ELECTRONS, so its valency is 4. The element Y has 6 valence electrons, so its valency is 2. So, one ATOM of element X will combine with two atoms of element Y to form a covalent compound having the formula `XY_(2)`.
Discussion
2356.

There are three elements X, Y and Z having atomic numbers of 6, 16 and 19 respectively. Based on this information, Het has been asked to answer the following questions: Which two elements will form covalent bonds? Why?

Answer»

Solution :In order to answer these questions, Het first wrote down the ELECTRONIC configurations of the ELEMENTS X, Y and Z by using their atomic numbers, as follows:
(4)
A covalent BOND is formed between two non-metallic elements. Here, element X of group 14 is a non-metal and element Y of group 16 is also a non-metal. Therefore, the elements X and Y will combine together to FORM covalent bonds.
Discussion
2357.

There are three elements X, Y and Z having atomic numbers of 6, 16 and 19 respectively. Based on this information, Het has been asked to answer the following questions: What will be the formula of ionic compound formed ?

Answer»

Solution :In order to answer these questions, Het first wrote down the electronic configurations of the elements X, Y and Z by using their atomic numbers, as follows:

(3) The element Z has 1 valence ELECTRON, so its valency is +1 (after losing this electron). The element Y need two electrons to complete its OCTET. So, element Y will gain two electrons and form `Y^(2-)` ion. Here, two `Z^(+)` IONS will combine with one `Y^(2-)` ion, so that the FORMULA of ionic compoundformed will be `Z_(2)Y`.
Discussion
2358.

There are three elements X, Y and Z having atomic numbers of 6, 16 and 19 respectively. Based on this information, Het has been asked to answer the following questions: Which two elements will form ionic bonds? Why?

Answer»

Solution :In order to answer these QUESTIONS, Het FIRST wrote down the electronic configurations of the elements X, Y and Z by using their atomic numbers, as FOLLOWS:

(2) An IONIC BOND is formed between a metal element and a non-metal element. Here, the elements Z and Y will combine to form ionic bond.
Discussion
2359.

There are three elements X, Y and Z having atomic numbers of 6, 16 and 19 respectively. Based on this information, Het has been asked to answer the following questions: In which group of the periodic table would you expect to find (i) element x (ii) element Y and (iii) element z?

Answer»

Solution :In ORDER to ANSWER these questions, Het first wrote down the electronic configurations of the ELEMENTS X, Y and Z by using their atomic numbers, as follows:

(1) (i) Element X has 4 valence electrons in its atom, so it will be placed in group 4 + 10 = 14 of the modern periodic table.
(II) Element Y has 6 valence electrons in its atom, so it will be placed in group 6 + 10 = 16 of the modern periodic table.
(iii) Element Z has 1 valence electron in its atom, so it will be placed in group 1 of the modern periodic table.
Discussion
2360.

Write the formula and name ofproduct in theReaction of ethanol with sodium.

Answer»

SOLUTION :`2C_2H_5OH L) + 2NA(s) to 2C_2H_5ONa + H_2(G)`
Discussion
2361.

Two elements M and N beong to group I and II respectively and are in the same period of the periodic tabe. How do the follwoing properties of M and N vary ? Their metallic characters

Answer»

SOLUTION :M is more METALLIC than N
Discussion
2362.

Two elements M and N beong to group I and II respectively and are in the same period of the periodic tabe. How do the follwoing properties of M and N vary ? Molarcular formulae of their chlorides

Answer»

SOLUTION :MCL and `NCl_2`
Discussion
2363.

Two elements M and N beong to group I and II respectively and are in the same period of the periodic tabe. How do the follwoing properties of M and N vary ? Their valencies in forming oxides

Answer»

SOLUTION :M has a VALENCY of 1 and N has a valency of 2
Discussion
2364.

The statement given below are the postulates of various atomic models . Arrange them in their chronological order Fine structure is due to the presence of subshells in the main energy level The size of an atom is much larger than the size of its nucleus As long as the electron is present in a particular orbit , its energy remains constant Negative charged particals are uniformly spread inthe lump of positive charge

Answer»

4,3,2,1
2,3,4,1
4,2,3,1
3,4,2,1

Solution :Negatively charged particles are uniformly spread in the lump of positive charge (Thomson s MODEL).
The SIZE of atom is much LARGER than the size of its nucleus (Rutherford's model).
As long as the electron is present in a particular orbit, its energy remains constant (BOHR's model).
Fine structure is due to the presence ofsubshells in the main energy LEVEL (Sommerfeld s model).
Discussion
2365.

What is the number of iron atoms and hydrogen atoms in the balanced equation for the reaction of steam on iron ?

Answer»

3Fe and 8 H
3Fe and 4H
3Fe and 6H
3Fe and 10H

Solution :The BALANCED EQUATION for the reaction is
`3Fe+4H_(2)OtoFe_(3)O_(4)+4H_(2)`
Discussion
2366.

XeF_(2) is also a linear molecule like BeCl_(2). But they differ in their formation and structural aspects. How can you justify this?

Answer»

Solution :(i)comparison of ELECTRONIC CONFIGURATION of beryliumand xenon
(ii) type of hybridisation in `XeF_(2)` and `BeCl_(2)`
(iii) the NUMBER of LONE pairs and bond pairs present in the valence shell of the central atom
Discussion
2367.

What are structural isomers ? Give examples.

Answer»

SOLUTION :Compounds having the same molecular formula but different STRUCTURAL formulae are known as structural isomers.
Examples :
(1) Structural isomers of butane `(C_(4)H_(10))` :

(2) Structural isomers of pentane `(C_(5)H_(12))` :
(a) `CH_(3)-CH_(2)-CH_(2)-CH_(2)-CH_(3)`n-Pentane (Pentane)
(b) `CH_(3)-underset(CH_(3))underset(|)CH-CH_(2)-CH_(3)`Isopentane (2-Methylbutane)
( c ) `CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-CH_(3)`Neopentane (2, 2-Dimethyl-propane)
(3) Structur5al isomers of hexane `(C_(6)H_(14))` :
(a) `CH_(3)-CH_(2)-CH_(2)-CH_(2)-CH_(2)-CH_(3)`n-Hexane (Hexane)
(b) `CH_(3)-underset(CH_(3))underset(|)CH-CH_(2)-CH_(2)-CH_(3)`2-Methylpentane
( c ) `CH_(3)-CH_(2)-underset(CH_(3))underset(|)CH-CH_(2)-CH_(3)`3-Methylpentane
(d) `CH_(3)-underset(CH_(3))underset(|)CH-underset(CH_(3))underset(|)CH-CH_(3)`2, 3-Dimethylbutane
(e) `CH_(3)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-CH_(2)-CH_(3)`2,2-Dimethylbutane
Discussion
2368.

Which one of the following is an unsaturated hydrocarbon?

Answer»

Acetylene
Butane
Propene
Decane

Answer :A
Discussion
2369.

Whatis Cast iron ?

Answer»

SOLUTION :The PIGIRON is remeltedand CAST into differentmoulds. This IRON is CALLED cast iron .
Discussion
2370.

Which of the following phenomena occur, when a small amount of acid is added to water? (i) Ionisation, (ii) Neutralisation, (iii) Dilution, (iv) Formation

Answer»

(i) and (II)
(i) and (iii)
(ii) and (iii)
(ii) and (iv)

Solution :(i) When water is ADDED to an acid, the molecules DISSOCIATE to from ions
`HCl+H_(2)OrarrH^(+)+Cl^(-)+H_(2)O`
`H_(2)O+H^(+)rarrH_(3)O^(+)`(Hydronium ion)
(ii) Mixing of an acid with water is called DILUTION, it results in the decrease in the concentration of ions, `(H_(3)O^(+))` per unit volume.
Discussion
2371.

Which of the statements about the reaction below are incorrect ? 2PbO(s)+C(s)to2Pb(s)+CO_(2)(g)

Answer»

Lead is getting REDUCED.
Carbon DIOXIDE is getting OXIDIZED.
Carbon is getting oxidized.
Lead dioxide is getting reduced.

ANSWER :A::B::C::D
Discussion
2372.

Write the name and symbols of two most reactive metals. Explain by drawing electronic structure how any one of the two metals react with a halogen. State any four physical properties of the compound formed.

Answer»

Solution :The two reactive metals are sodium (Na) and potassium (K).
`{:(Na,rarr,Na^(+)+e^(-),),("2,8,1",,"2,8",),(,,"(Sodium cation)",):}`
`{:(CL,rarr,Cl^(-),),("2,8,7",,"2,8,8",),(,,"(Chloride anion)",):}`

PHYSICAL property of compound form :
(i) Ionic compounds have high melting and boiling points.
(ii) They are good conductors of electricity.
(iii) They are GENERALLY soluble in water and INSOLUBLE in organic solvents.
(iv) They are solids, hard and brittle.
Discussion
2373.

Unsaturated hydrocarbons gives a ......... flame with lots of ......... smoke.

Answer»

SOLUTION :YELLOW, BLACK
Discussion
2374.

When the electrons are successively filled in the orbitals of same shell, orbital, Which is filled at the end, requires less energy to remove electron. Justify.

Answer»

SOLUTION : REQUISITE FER FILLING up of ORBITALS.
Discussion
2375.

Write the general information of the modern periodic table.

Answer»

Solution :In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.
Accordingly, “Mendeleev.s periodic law. was modified to .Modern periodic law and atomic number was adopted as basis to form modern periodic table.
Modern periodic law : "PROPERTIES of elements are a periodic function of their atomic number."
The atomic number of any element is equal to the number of PROTONS in the NUCLEUS of the atom.
In modern periodic table, elements are arranged in order of INCREASING atomic numbers, hence PREDICTION of properties of elements could be made with more accuracy.
Modern periodic table accounted the all three limitations of Mendeleev.s periodic table.
Discussion
2376.

Which of the following compounds in solution will make blue litmus paper red ?

Answer»

`NH_(2)OH`
`HCl`
`H_(2)O`
`NAOH`

Answer :B
Discussion
2377.

What are the products of electrolysis of (i) concentrated KBr and (ii) dilute KBr solution ? Give reasons in support of your answer

Answer»

Solution :(i) Preferential discharge of ions.
(II) The various ions present in the RESPECTIVE solution.
(iii) Factors responsible for the products OBTAINED at the two electrodes
(iv) The RELATIVE domination of various factors and their effect on the products produced
Discussion
2378.

What happens when the surface of sample of metal is rubbed with sand paper ?

Answer»

Solution : When the surface of SAMPLE of METAL is rubbed with SAND paper, it appears SHINY.
Discussion
2379.

What is meant by refining of metals? Describe the electrolytic refining of copper with a neat labelled diagram.

Answer»

Solution :In electrolytic refining process, the impure metal is MADE as ANODE and a thin strip of pure metal is made as cathode. A solution of the metal salt is made as an electrolyte. On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte. AN equivalent amount of pure metal from the electrolyte is deposited on the cathode.The SOLUBLE impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are KNOWN as anodemud.
At anode: `CU to Cu^(2+)+2e^(-)`
At cathode: `Cu^(2+)+2e^(-) to Cu`
Discussion
2380.

The strategic metals such as copper , silver and gold are used in the manufacturing of defence equipments

Answer»


SOLUTION :The strategic metals such as titanium, CHROMIUM MANGANESE, ZIRCONIUM are used in the manufacturing of defence equipments.
Discussion
2381.

What is the use of catalytic convertic in automobile exhaustsystems ?

Answer»

SOLUTION :(i) gases produced during comubstion of fuels
(ii) nature of gases that are liberated through an exhaust SYSTEM.
(iii) role of catalytic CONVERTER for changing the molecules compositioin of the exhaust gases
(iv) change in nature of the gases DUE to the change in the molecules composition
Discussion
2382.

What happens when a solution of an acid is mixed with a solution of a base in a test tube ? (i) The temperature of the solution increases (ii) The temperature of the solution decreases (iii) The temperature of the solution remains the same. (iv) Salt formation takes place.

Answer»

Only (i)
(i) and (iii)
(ii) and (iii)
(i) and (iv)

Solution :When an ACID REACTS with a base, NEUTRALISATION reaction takes place to form salt and water and it is an EXOTHERMIC reaction. So the TEMPERATURE of the solution increases
Discussion
2383.

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

Answer»

SOLUTION :In TARNISHED copper vessel there is a layer of BASIC copper carbonate. This basic layer can be cleaned by using sour substances such as lemon or tamarind JUICE which are ACIDIC in nature and dissolve the basic coat of copper carbonate.
Discussion
2384.

What would you take as the anode, the cathode and the electrolyte in the electrolytic refining of metal M?

Answer»

SOLUTION :ANODE: A thick BLOCK of impure metal M
Cathode: A thin STRIP of the pure metal M
Electrolyte : A water SOLUBLE salt of the metal M.
Discussion
2385.

Which of the following is generally true.A: Atomic size increases from left to right across a period. B: Ionization potential increases from left to right across a period.C: Electron affinity increases on going down a group. D: Electronegativity increases on going down a group.

Answer»

Atomic size DECREASES from left to right ACROSS a period.
Electron affinity decreases on going down a GROUP.
Metallic character decreases from left to right across a period.
ELECTRONEGATIVITY increases on going down a group.

Solution :Electronegativity increases on going down a group.
Discussion
2386.

To obtain a diminished image of an object from a concave mirror, position of the object should be (F = principal focus , C = centre of curvature. P - pole)

Answer»

<P>between C and F
beyond C
between P and F
at F

Answer :B
Discussion
2387.

Write the name the following functional group -OH" "

Answer»

SOLUTION :a] ALCOHOL B] KETONE .
Discussion
2388.

What is the maximum length of wire which can be drawn from one gram of gold ?

Answer»

SOLUTION :2 KM LENGTH
Discussion
2389.

Write the reaction of chlorine with ethynein the absence of light

Answer»

SOLUTION :`HC -= CH overset(Cl_2)(to) ClHC = CHCL overset(Cl_2)(to) Cl_2HC - CHCl_2`
Discussion
2390.

What happens when hydrate copper sulphate is heated ?

Answer»

it becomes colourless
it turns into ANHYDROUS SALT
it loses water of crystallization
all of the above

Solution :`{:(underset("hdydrated salt (blue)")(CuSO_4 * 5 H_2 O) overset("Heat")to underset("PALE blue")(CuSO_4 * H_2 O)),(""darr "Heat"),(""underset("colouless")underset("anhydrous")(CuSO_4)):}`
Discussion
2391.

Which metal does not react with hydrochloric acid ?

Answer»

SOLUTION :COPPER (Cu) METAL do not react with HYDROCHLORIC ACID.
Discussion
2392.

Which among the folowing is double displacement reaction(s) ? "(i) "Pb+CuCl_(2)toPbCl_(2)+Cu"(ii) "Na_(2)SO_(4)+BaCl_(2) to BaSO_(4)+2NaCl " (iii) "C+O_(2)toCO_(2)"(iv) "CH_(4)+2O_(2) to CO_(2)+2H_(2)O

Answer»

(i) and (IV)
(II) only
(i) and (ii)
(iii) and (iv)

SOLUTION :The ANIONS and cations are exchanged in the reaction (ii) only.
Discussion
2393.

What happens chemically when quicklime is added to water filled in a bucket ?

Answer»

Solution :When QUICK lime is added to water slaked lime is formed with hissing sound ALONG with liberation of LARGE AMOUNT of heat :
`CaO(s)+H_(2)O(l)toCa(OH)_(2)(aq)`.
Discussion
2394.

Zinc liberates hydrogen gas when reacted with dilute nitric acid whereas copper does not. Why ?

Answer»

Solution :Zinc is more reactive than hydrogen and hence it DISPLACES hydrogen from dilute HCl, WHEREAS COPPER is less reactive than hydrogen hence it does not SHOW any reaction.
Discussion
2395.

Three elements having 7 electrons in theiroutermost shell.

Answer»

Solution :(i) FLUORINE (2,7) (ii) CHLORINE (2,8,7) (iii) BROMINE(2,8, 18,7).
Discussion
2396.

Valency

Answer»

SOLUTION :CARBON, SILICON.
Discussion
2397.

Which of the following oxide is most acidic?

Answer»

`Na_2O `
`Al_2O_3
`P_2O_5`
`SO_3`

ANSWER :D
Discussion
2398.

Zinc blende is a _________ ore .

Answer»

SOLUTION :SULPHIDE
Discussion
2399.

What is the colour of the light produced when magnesium burns in air ?

Answer»

SOLUTION :DAZZLING WHITE.
Discussion
2400.

When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding potassium metal to water catches fire. Explain why ?

Answer»

SOLUTION :In both cases, the gas evolved is `H_(2)`. When calcium reacts with water the heat evolved is not sufficient for hydrogen to CATCH FIRE. On the other hand, potassium reacts with water violently and lot of heat is evolved which is sufficient for hydrogen to catch fire.
Discussion