2021 The p-Block Elements (Group 15 to 18)Groups 15, 16 and 17 – Trends in Hydrides and Oxides Hard Question 6 of 11 in The p-Block Elements (Group 15 to 18)

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

A $H_2O<H_2S<H_2Se<H_2Te$ : Increasing $pK_a$ values
B $NH_3<PH_3<AsH_3<SbH_3$ : Increasing acidic character
C $CO_2<SiO_2<SnO_2<PbO_2$ : Increasing oxidising power
D $HF<HCl<HBr<HI$ : Increasing acidic strength

The answer is A.

Solution

Down group 16, acidic strength increases: $H_2O < H_2S < H_2Se < H_2Te$, so $pK_a$ decreases (not increases). So '$H_2O < H_2S < H_2Se < H_2Te$ : increasing $pK_a$' is not correct. The other sequences are correct.

Concept periodic trends in acidity and oxidising power

The p-Block Elements (Group 15 to 18) in past papers

11 questions from this chapter have appeared across 5 exam years.