Chemistry 12 Chapter 7 Exemplar Solutions the P Block Elements Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 53:

Name three oxyacid՚s of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in oxidation state.


Three oxoacids of nitrogen are

(i) , Nitrous acid

(ii) , Nitric acid

(iii) Hyponitrous acid,

Question 54:

Nitric acid forms an oxide of nitrogen on reaction with . Write the reaction involved. Also write the resonating structures of the oxide of nitrogen formed.


Nitric Acid

Question 55:

Phosphorus has three allotropic forms — (i) white phosphorus (ii) red phosphorus and (iii) black phosphorus. Write the difference between white and red phosphorus on the basis of their structure and reactivity.


(a) • Structures (See NCERT textbook for Class XII)

• White phosphorus is discrete tetrahedral molecule. Thus it has tetrahedral structure with six bonds.

• Red phosphorus has polymeric structure in which tetrahedra are linked together through bonds to form chain.

(b) Reactivity

White phosphorus is much more reactive than red phosphorus. This is because in white phosphorus there is angular strain in molecules because the bond angles are only of .

Question 56:

Give an example to show the effect of concentration of nitric acid on the formation of oxidation product.


Dilute and concentrated nitric acid give different oxidation products on reaction with copper metal.

Question 57:

reacts with finely divided silver on heating and a white silver salt is obtained, which dissolves on adding excess aqueous solution. Write the reactions involved to explain what happens.


Question 58:

Phosphorus forms a number of oxoacids. Out of these oxoacids phosphinic acid has strong reducing property. Write its structure and also write a reaction showing its reducing behaviour.


Structure of phosphinic acid (Hypophosphorous acid) is as follows:

Phosphinic Acid

Reducing behaviour of phosphinic acid is observable in the reaction with silver nitrate given below:

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