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Chapter: 12th Chemistry : UNIT 3 : p-Block Elements-II

p-Block Elements-II: Answer the following questions

Chemistry : p-Block Elements-II: : Book Back Important Questions, Answers, Solutions : Answer briefly, Answer in detail, Exercise Numerical Problems

Chemistry : p-Block Elements-II

Answer the following questions:

1.     What is inert pair effect?

In p-block elements in the case of post -- transition elements belonging to group number 13 to 16, the most stable oxidation state is two less than the group oxidation state due to the inert tendency of ns electrons to take part in chemical bonding. This effect is known as inert pair effect.

2.     Chalcogens belongs to p-block. Give reason.

Chalcogens have general electronic configuration ns2, np4. The added electrons filled in the p orbital. Hence it belong to p-block.

The elements of chalgogens have similar outer shell electronic configuration and differ only in the value of n (principal quantum number).

3.     Explain why fluorine always exhibit an oxidation state of -1?

Due its more electronegativity it always accepts one electron in its valence shell. Hence it always exhibits an oxidation state of −1. It will not lose electron from its outermost shell. Therefore it will not exhibit positive oxidation state.

4.     Give the oxidation state of halogen in the following.

a) OF2 b) O2F2 c) Cl2O3 d) I2O4

a) OF2 : −1

b) O2F2 : −1

c) Cl2O3 : +3

d) I2O4 : +4

5.        What are interhalogen compounds? Give examples.

Each halogen combines with other halogens to form a series of compounds called inter halogen compounds.

Example: AB type - ClF

 AB3 type - ClF3, ICl3

6.     Why fluorine is more reactive than other halogens?

Due to low bond dissociation energy and more electronegativity fluorine is more reactive than other halogens.

7.     Give the uses of helium.

1. Helium and oxygen mixture is used by divers in place of air oxygen mixture. This prevents the painful dangerous condition called bends.

2. Helium is used to provide inert atmosphere in electric arc welding of metals

3. Helium has lowest boiling point hence used in cryogenics.

4. It is much less denser than air and hence used for filling air balloons

8.     What is the hybridisation of iodine in IF7? Give its structure.

The hybridisation of iodine in IF7 is sp3d3

Structure of IF7 is pentagonal bipyramidal

9.     Give the balanced equation for the reaction between chlorine with cold NaOH and hot NaOH.

Cold NaOH

Chlorine reacts with cold dilute alkali to give chloride and hypochlorite

Cl2 + 2NaOH → NaOCl + NaCl + H2O

NaOCl : Sodium hypo chlorite

Hot NaOH

Chlorine reacts with hot concentrated alkali to give chlorides and chlorates

3Cl2 + 6NaOH → NaClO3 + 5NaCl + 3H2O

10. How will you prepare chlorine in the laboratory?

Chlorine is prepared by the action of conc. sulphuric acid on chlorides in presence of manganese dioxide.

4NaCl + MnO2 + 4H2SO4 → Cl2 + MnCl2 + 4NaHSO4 + 2H2O

Chlorine is liberated when bleaching powder is treated with mineral acids

CaOCl2 + 2HCl → CaCl2 + H2O + Cl2

CaOCl2 + H2SO4 → CaSO4 + H2O + Cl2

Chlorine is prepared by oxidising hydrochloric acid using various oxidising agents

PbO2 + 4HCl → PbCl2 + 2H2O + Cl2

11. Give the uses of sulphuric acid.

i) Sulphuric acid is used in the manufacture of fertilisers, ammonium sulphate and super phosphates and other chemicals such as hydrochloric acid, nitric acid etc

ii) It is used as a drying agent and also used in the preparation of pigments, explosives etc

12.   Give a reason to support that sulphuric acid is a dehydrating agent.

Sulphuric acid removes water from many organic compounds.

C12H22O11 + H2SO4 → 12C + H2SO4 . 11H2O

 HCOOH + H2SO4 → CO + H2SO4 .H2O


13. Write the reason for the anamolous behaviour of Nitrogen.

Small size

High value of electronegativity

High ionisation enthalpy

Absence of d-orbital

14. Write the molecular formula and structural formula for the following molecules.

a) Nitric acid

b) dinitrogen pentoxide

c) phosphoric acid

d) phosphine

15. Give the uses of argon.

Argon prevents the oxidation of hot filament and prolongs the life in filament bulbs

16. Write the valence shell electronic configuration of group-15 elements.

The general valence shell electronic configuration of group−15 element is ns2np3

Nitrogen 2s22p3

Phosphorous 3s23p3

Arsenic 4s24p3

Antimony 5s25p3

Bismuth 6s26p3

17. Give two equations to illustrate the chemical behaviour of phosphine.

When phosphine is heated with air or oxygen it burns to give meta phosphoric acid.

4PH3 + 8O2 __Δ_→ P4O10 + 6H2O

P4O10 + 6H2O __Δ_ → 4HPO3 + 4H2O

Phosphine precipitates metal from their salt solutions.

3AgNO3 + PH3 → Ag3P + 3HNO3

18. Give a reaction between nitric acid and a basic oxide.

Nitric acid reacts with basic oxides to form salts and water

3FeO + 10HNO3 → 3Fe(NO3)3 + NO + 5 H2O

19. What happens when PCl5 is heated?

On heating phosphorous pentachloride decomposes into phosphorus trichloride and chlorine.

PCl5 → PCl3 + Cl2

20. Suggest a reason why HF is a weak acid, whereas binary acids of the all other halogens are strong acids.

Hydrochloric, hydrobromic and hydroiodic acids are almost completely ionized and they are strong acids. 0.l mM solution of HF ionized only 10%, therefore it is weak acidic.

21. Deduce the oxidation number of oxygen in hypofluorous acid – HOF.

HOF = +l + x – l = 0

Oxygen exhibits zero state in hypofluorous acid


22. What type of hybridisation occur in

a) BrF5 b) BrF3


a) BrF5 - sp3d2

b) BrF3 - sp3d

23.   Complete the following reactions.

1.        NaCl + MnO2 + H2SO4 

2.        NaNO2 + HCl 

2.        IO3 + I + H+ 

3.        I2 + S2O32 

4.        P4 + NaOH + H2

5.        AgNO3 + PH3 

6.        Mg + HNO3 

7.        KClO3 Δ hot conc.

8.        Cu + H2 SO4

9.        Sb + Cl2 

10.   HBr + H2SO4 

11.   XeF6 + H2O

12.   XeO64 + Mn2+ + H+ 

13.   XeOF4 + SiO2 

14.   Xe + F2 


1. 4NaCl + MnO2 + 4H2SO4 → Cl2 + MnCl2 + 4NaHSO4 + 2H2O

2. NaNO2 + HCl → NaCl + HNO2

3. IO3 +5I+ 6H+ → 3I2 + 3H2O

4. I2 + 2S2O32− → S4O62− + 2I

5. P4 + 3NaOH + 3H2O → 3NaH2PO2 + PH3

6. 3AgNO3 + PH3 → Ag3P + 3HNO3

7. 4Mg + 10HNO3 → 4Mg(NO3)2 + N2O + 5H2O

8. 2KClO3 ___Δ   Hot conc.__→ 2KCl + 3O2

9. Cu + 2H2SO4 → CuSO4 + 2H2O + SO2

10. 2Sb + 3Cl2 → 2SbCl3

11. 2HBr + H2SO4 → SO2 + 2H2O + Br2

12. XeF6 + 3H2O → XeO3 + 6HF

13. 5XeO64− + 2Mn2+ + 14H+ → 2MnO4 + 5XeO3+ 7H2O

14. 2XeOF4 + SiO2 → 2XeO2F2 + SiF4

15. Xe + 3F2 __Ni/200 atm_400oC__→ XeF6



l. Write the products formed in the reaction of nitric acid (both dilute and concentrated) with zinc.

Zinc reacts with HNO3 at various concentrations and it gives different products.

4 Zn + 10 HNO3 (dil)


4 Zn (NO3)2 [Zinc nitrate] + N2O [Nitrous oxide] + 5 H2O


4 Zn + 10 HNO3 (very dilute)


 4 Zn (NO3)2 [Zinc nitrate] + NH4NO3 [Ammonium nitrate] + 3H2O


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