Solved: CHEMISTRY Question for NEET

NEET CHEMISTRYMedium

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

$\text{HF} < \text{HCl} < \text{HBr} < \text{HI}$ : Increasing acidic strength

$\text{H}_2\text{O} < \text{H}_2\text{S} < \text{H}_2\text{Se} < \text{H}_2\text{Te}$ : Increasing $\text{pK}_a$ values

$\text{NH}_3 < \text{PH}_3 < \text{AsH}_3 < \text{SbH}_3$ : Increasing acidic character

$\text{CO}_2 < \text{SiO}_2 < \text{SnO}_2 < \text{PbO}_2$ : Increasing oxidizing power

Step-by-Step Solution

Stronger is the acid, lower is the value of $\text{pK}_a$ . On moving down the group, bond dissociation enthalpy of hydrides of group 16 elements decreases, hence acidity increases and $\text{pK}_a$ value decreases. The correct order of $\text{pK}_a$ value is $\text{H}_2\text{O} > \text{H}_2\text{S} > \text{H}_2\text{Se} > \text{H}_2\text{Te}$ .

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