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When iron is exposed to moist air, it forms a layer of brown hydrated ferric oxide on its surface. This compound is known as rust and the phenomenon of formation of rust is known as rusting. 

4Fe + 3O₂ + xH₂O → 2Fe₂O₃ . xH₂O (Rust)

Corrosion of metals is prevented 

• by coating with paints
• by coating with oil and grease 
• by alloying with other metals 
• by the process of galvanization 
• by electroplating 
• by sacrificial protection

(c) Fe₂O₃ . xH₃O 

On heating at 800°C, aluminium bums in the air very brightly forming its oxide and nitride. 

4Al + 3O₂ → 2Al₂O₃ (Aluminium oxide) 

2Al + N₂ → 2AlN (Aluminium nitride)

(i) The slow and steady destruction of a metal by chemical

or electro chemical reaction with the environment. 

(ii) When the surface of iron is exposed to moisture and other gases present in the atmosphere, the following chemical reaction takes place. 

Fe → Fe²⁺ + 2e^- 

O₂ + 2H₂O + 4e^- → 4OH^- 

O₂ + 4H⁺ + 4e^- → 2H₂O 

The Fe²⁺ ions are oxidised to Fe³⁺ ions.

The Fe³⁺ ions combine OH^- ions to form Fe(OH)₃ . This becomes rust which is hydrated ferric oxide with the formula Fe₂O₃.xH₂O. It is a reddish brown substance.

Aluminium is used in 

1. household utensils 

2. electrical cable industry 

3. making aeroplanes and other industrial machine parts.

Wood metal is an alloy of Lead, Tin, Bismuth and Cadmium.

(i) Pig iron (Iron with 2-4.5% of carbon): It is used in making pipes, stoves, radiators, railings, manhole covers and drain pipes. 

(ii) Steel (Iron with < 0.25% of carbon): It is used in the construction of buildings, machinery, transmission cables and T. V towers and in making alloys.

(iii) Wrought iron (Iron with 0.25-2% of wraught carbon): It is used in making springs, anchors and electromagnets.

Cathode: A thin plate of pure copper metal. 

Anode: A block of impure copper metal. 

Electrolyte: Copper sulphate solution + dilute H₂SO₄ When an electric current is passed through the electrolytic solution, pure copper gets deposited at the cathode and the impurities are settled at the bottom of the anode as anode mud.

In a period, from left to right the electronegativity increases because of the increase in the nuclear charge. In a Group, from top to bottom, the electronegativity decreases because of the increase in size of the elements.

Group number of carbon family is 14

1. NH₄NO₃ 

2. 3SO₂

The shortest period in the periodic table contains elements is 2

• In a period, the electrons are filled in the same valence shell of all elements. 
• As the electronic configuration changes along the period, the chemical properties of the elements also change. 
• The atomic size of the elements in a period decreases from left to right 
• In a period, die metallic character of the element decreases, while their non-metallic character increases.

The largest atom in the 2nd period of the periodic table is Li

The horizontal rows are called periods.There are seven periods in the periodic table. 

1. First period (Atomic number 1 and 2): This is the shortest period. It contains only two elements (Hydrogen and Helium). 

2. Second period (Atomic number 3 to 10): This is a short period. It contains eight elements (Lithium to Neon).

3. Third period (Atomic number 11 to 18): This is also a short period. It contains eight elements (Sodium to Argon). 

4. Fourth period (Atomic number 19 to 36): This is a long period. It contains eighteen elements (Potassium to Krypton). This includes 8 normal elements and 10 transition elements. 

5. Fifth period (Atomic number 37 to 54): This is also a long period. It contains 18 elements (Rubidium to Xenon). This includes 8 normal elements and 10 transition elements. 

6. Sixth period (Atomic number 55 to 86): This is the longest period. It contains 32 elements (Caesium to Radon). This includes 8 normal elements, 10 transition elements and 14 inner transition elements (Lanthanides). 

7. Seventh period (Atomic number 87 to 118): Like the sixth period, this period also accommodates 32 elements. Recently 4 elements have been included by IUPAC.

(i) Sodium

(ii) Aluminium

(iii) Magnesium

(iv) Nickel steel

Na (Sodium), Mg (Magnesium) and Al(Aluminium) are metals. Si (Silicon) is a metalloid. P (Phosphorus), S (Sulphur) and Cl (Chlorine) are non-metals.

As we go from left to right across the third period, metallic character decreases and non-metallic character increases.

The most metallic element in the third period is Na and the most non-metallic element is Cl.

The above elements belong to period 2.

The above elements belong to group 1.

1. Sodium 

2. Magnesium 

3. Aluminum.

i. Group 1.

ii. Phosphorus, sulfur and chlorine, and argon.

iii. Carbon. silicon.

iv. Helium, neon, and argon.

The chemical formula of its chloride is AlCl₃

(i) The electronic configuration tells about the number of electrons present in different shells. Thus total electrons can be found by adding the electrons present in all shells i.e. 2+8+6=16. The number of electrons and protons are equal. Therefore, atomic number is 16. 

(ii) The element with atomic number(Z)=16 is sulphur. The other element which show chemical similarity with sulphur is oxygen.

(i) Both Na and K belongs to the same group (group I). Both contains same number of electrons in their valence shells i.e. 1 

(ii) Both B and C belong to the same period (2nd period). Both contains same number of shells i.e. 2

(i) X-2,5: Group 15

Y-2,8: Group 18

Z-2, 8,4: Group 14

(ii) Y is a noble gas which is unreactive and has a complete outermost shell.

Z is metalloid and possesses semi-metal, properties of both metals and non-metals.

(iii) X and V belong to the same period i.e., 2^nd period.

In the third period of the Periodic Table the element having smallest size is Ar.

i. Helium(He).

ii. Hydrogen(H₂).

iii. Fluorine(F₂).

iv. Helium(He).

v. Fluorine(F₂).

The atomic size increases on moving down the group. This is because of the increase in number of shells due to which the distance between the outermost electron and the nucleus increases.

The atomic size decreases on moving along a period. This is because of the increase in the effective nuclear charge on moving from left to right which tends to pull the electrons towards the nucleus.

Since the metal M belongs to the Group 13, so its valence shell will have 3 electrons. Thus the valency of the metal M belonging to 13^th group is 3.

(i) Element -E

(ii) k=2,l=8,M=6

(iii) X and Z.

(a) Sugar is used by athletes because: 

i. It is a multipurpose, an all-rounder fruit. 

ii. It can be used by athletes as high calorie fruit for high energy. 

iii. It increases the flow of blood in the whole body. 

iv. It increases haemoglobin too. 

(b) We should use sugar apple as a pesticides and insecticides instead of chemicals because: 

i. Chemicals can harm plants and can stop their growth. 

ii. On the other hand, the powdered seeds of sugar apple do not cause any harm to plants as they are purely natural. 

(c) Iron is present in our haemoglobin. Iron is an important element for the formation of blood in the body. The lack of iron in body can cause too many problems. The other fruits which is rich in iron is banana. 

(d) People take fruits rich in iron because iron increases the production of blood in the body. It increases the haemoglobin which keeps us fit from top to bottom 

(e) Seema is health-conscious, aware and knowledgeable too.

Electropositive character of elements decreases in a period because effective nuclear charge increases from left to right in a period. Due to this effective nuclear charge, the electronegativity increases and the attraction of nucleus on valence shell electrons also increases. So the tendency of losing electrons decreases. Hence the electropositive character of elements decreases in a period. 

Note- Non-metals always gain electrons and metals lose their electrons.

(i) Atomic radius decreases. 

(ii) Metallic character decreases.

There are 7 horizontal rows known as periods, that the modern periodic table has. 

In periods, the number of valence electrons increases from left to right and due to decrease in atomic size, the force of attraction between the valence electrons and the nucleus increases. Metallic character decreases along the period due to decrease in the tendency to lose electrons. 

Atomic size generally increases from top to bottom in a group due to the addition of a new shell i.e., the number of shells goes on increasing down the group

Atomic number.

Metallic character increases down a group because the size of elements increases down a group due to increment in the shells. So the effective nuclear charge decreases down a group. Due to this effective nuclear charge, the electronegativity decreases and the attraction of nucleus on valence shell electrons also decreases. So the tendency of losing electrons increases. Hence metallic character increases down a group.

Non- metallic character increases from left to right in a period because effective nuclear charge increases from left to right in a period. Due to this effective nuclear charge, the electronegativity increases and the tendency of gaining electrons also increases. So non- metallic character increases from left to right in a period.

Note- 

(i) Effective nuclear charge is defined as the charge per unit volume. 

(ii) From left to right in a period, the effective nuclear charge increases because charge increases from left to right due to increment of proton. But the size remains same because number of shells remains same from left to right in a period. 

(iii) From top to bottom in a group, the effective nuclear charge decreases because charge increases down a group due to increment of proton and the size of elements also increases due to increment in shells.

Down the group, the effective nuclear charge experienced by the valence electron decreases because the outer most electron are further away from the nucleus. Therefore, they can be lost easily. Hence metallic character increases down the group.

(i) From top to bottom in group - metallic character increases. 

(ii) From left to right in a period - metallic character decreases.

Joseph Priestley (1770) : Showed that plants have the ability to take up CO₂ from atmosphere and release O₂. 

Jan Ingenhousz (1779) : Release of O₂ by plants was possible only in sunlight and only by the green parts of plants. 

Theodore de Saussure (1804) : Water is an essential requirement for photosynthesis to occur. 

Julius Von Sachs (1854) : Green parts in plant produce glucose which is stored as starch. 

T. W. Engelmann (1888) : The effect of different wavelength of light on photosynthesis and plotted the first action spectrum of photosynthesis. 

C. B. Van Niel (1931) : Photosynthesis is essentially a light dependent reaction in which hydrogen from an oxidisable compound reduces CO₂ to form sugar. He gave a simplified chemical equation of photosynthesis. 

Hill (1937) : Evolution of oxygen occurs in light reaction. 

Calvin (1954-55) : Traced the pathway of carbon fixation. 

Hatch and Slack (1965) : Discovered C₄ pathway of CO₂ fixation.

Because it has been already proved that oxygen evolved during photosynthesis comes from H₂O not from CO₂.

In case if 6H₂O is used then 6O₂ will not be released (only 3O₂ is produced).

So, 12H₂O produces 6O₂ and out of 12H₂ molecules 6H₂ is used in making of glucose and rest 6H₂ with oxygen of CO₂ form 6H₂O as product. 

Correct option: (C) g mol^-1