(a) Give reasons for the following :

(i) Sulphur in vapour state shows paramagnetic behaviour.

(ii) N-N bond is weaker than P-P bond.

(iii) Ozone is thermodynamically less stable than oxygen.

(b) Write the name of gas released when Cu is added to

(i) dilute HNO₃ and

(ii) conc. HNO₃

OR

(a) (i) Write the disproportionation reaction of H₃PO₃.

(ii) Draw the structure of XeF_4.

(b) Account for the following :

(i) Although Fluorine has less negative electron gain enthalpy yet F₂ is strong oxidizing agent.

(ii) Acidic character decreases from N₂O₃ to Bi₂O₃ in group 15.

(c) Write a chemical reaction to test sulphur dioxide gas. Write chemical equation involved.

(a) (i) The vapour state of Sulphur exists as S2 molecule and has two unpaired electrons in its antibonding π orbitals. Due to presence of these two unpaired electrons in vapour state of Sulphur, it shows paramagnetism.

(ii) N-N sigma bond is weaker than P-P sigma bond due to the small bond length between the nitrogen atoms. The non-bonding electrons (lone pair of electrons) of both the atoms repel each other making it weaker than P-P sigma bond. This is why the catenation tendency is not present in Nitrogen.

(iii) The ozone is thermodynamically less stable than oxygen because it conversion to oxygen results in ΔH= -ve and ΔS= +ve which overall results in to overall ΔG= -ve according to the equation ΔG= ΔH-TΔS and hence spontaneously ozone converts back to oxygen.

(b) (i) Nitrogen monoxide is released when Copper is added to dil HNO₃

(ii) Nitrogen dioxide is released when Copper is added to conc. HNO₃

OR

(a) (i) When H₃PO₃ is heated then H₃PO₃ is heated H₃PO₄ and PH₃ is obtained, in which P undergoes in both oxidation as well as reduction reaction.

4H₃PO₃→ 3H₃PO₄ + PH₃

(ii) XeF₄- structure of XeF₄ is square planar having 2 lone pairs and 4 bond pairs

(b) (i) The oxidising capability of a substance depends upon three factors: bond dissociation enthalpy, electron gain enthalpy and hydration energy.

Although electron gain enthalpy of fluorine is less negative, but due the small size of F its hydration energy is high. Also, bond dissociation enthalpy of F₂ molecule is low due to repulsion between lone pairs of two F-atoms which are quite closely place in the molecule. Therefore, F₂ is strong oxidizing agent.

(ii) Acidic character of oxides of group 15 decreases and basicity increases down the group. Down the group, atomic size increases, electronegativity decreases and metallic character increases. Oxides of N and P are acidic, oxides of As and Sb are amphoteric and oxides of Bi are basic.

(c) Sulfur dioxide gas turns acidified potassium dichromate(VI) solution from orange to green. Chromium is reduced from (VI) to (III)

K₂Cr₂O_7(aq) + 3SO_2(g) + H₂SO_4(aq)→Cr₂(SO₄)_3(aq) + K₂SO_4(aq) + H₂O_(l)