(a) Arrange the following in the order of property indicated for each set :
(i) `F_2,Cl_2,Br_2, I_2` - Increasing bond dissociation enthalpy .
(ii) HF, HCl ,HBr, HI - Decreasing acid strength
(iii) `NH_3 ,PH_3 , AsH_3, SbH_3, BiH_3` - Decreasing base strength .
(b) Write the conditions to maximize the yield to `H_2SO_4` by contact process .

Explanation

(a) (i) Increasing bond dissociation enthalpy
`I_2 lt F_2 lt Br_2 lt Cl_2`
(ii) Decreasing acid strength
HI > HBr > HCl > HF
(iii) Decreasing base strength
`NH_3 gt PH_3 gt AsH_3 gt SbH_3 gt BiH_3`
(b) Conditions for maximum yield of `H_2SO_4` by contact process
(i) Low temperature - 720 K
(ii) High pressure - 2 atm
(iii) Purity of gases
(iv) Presence of a catalyst `Pt//V_2O_3`
(v) An excess of `O_2`