Question

In which of the following arrangements, the sequence is not strictly according to the property written against it ?

• A. HF <HCl<HBr<HI : increasing acid strength
• B. NH3< PH3<AsH3<SbH3 : increasing basic strength
• C. B < C < O <N : increasing first ionization enthalpy
• D. CO2<SiO2<SnO2<PbO2 : increasing oxidising power

Answer 1

Answer: (B)

NH3< PH3<AsH3<SbH3 : increasing basic strength

Answer 2

HF < HCl < HBr < HI (on moving top to bottom, bond dissociation energy decreases, so acidic strength increases).

B < C < O < N (on moving left to right, Zeff increases, so first ionization enthalpy increases ; N > O because N is half filled).

CO2 < SiO2 < SnO2 < PbO2 (on moving top to bottom, + 4 oxidation state becomes less stable due to inert pair effect). So oxidising power increases.

Since, (1), (3) and (4) are correct, so (2) is the answer.

In hydrides of 15th group elements, the basic strength decreases down the group and the correct order is :

SbH3 < AsH3 < PH3 < NH3