Question

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

(a) HF < HCl < HBr < HI : increasing acidic strength

(b) H₂O < H₂S < H₂Se < H₂Te : increasing pK_a values

(c) NH₃ < PH₃ < AsH₃ < SbH₃ : increasing acidic character

(d) CO₂ < SiO₂ < SnO₂ < PbO₂ : increasing oxidising power

Answer 1

Correct option (b) H₂O < H₂S < H₂Se < H₂Te : increasing pK_a values

Explanation :

Acidic strength of hydrides increase with increase in molecular mass.

Thus order of acidic strength is

And as acidic strength increases, pK_a decreases. Thus order of pK_a

H₂O < H₂S < H₂Se < H₂Te