Q48 / 180 · AIIMS 2016 · Chemistry
Assertion : $\mathrm{H}_2 \mathrm{~S}$ is stronger acid than $\mathrm{PH}_3$.
Reason : $S$ is more electronegative than $\mathrm{P}$, conjugate base $\mathrm{HS}^{-}$is more stable than $\mathrm{H}_2 \mathrm{P}^{-}$.
- Correct answerAIf both assertion and reason are true and reason is the correct explanation of assertion.
- BIf both assertion and reason are true but reason is not the correct explanation of assertion.
- CIf assertion is true but reason is false.
- DIf both assertion and reason are false.
Solution
$\begin{aligned} & \mathrm{H}_2 \mathrm{~S}_{(g)}+a q \longrightarrow \mathrm{HS}_{(a q)}^{-}+\mathrm{H}_{(a q)}^{+} \\ & \mathrm{PH}_{3(g)}+a q \longrightarrow \mathrm{H}_2 \mathrm{P}^{-}+\mathrm{H}_{(a q)}^{+}\end{aligned}$
As $\mathrm{S}$ is more electronegative than $\mathrm{P}$, conjugate base $\mathrm{HS}^{-}$is more stable than $\mathrm{H}_2 \mathrm{P}^{-}$. Hence, $\mathrm{H}_2 \mathrm{~S}$ is stronger acid than $\mathrm{PH}_3$.
Hence, the correct answer is option: 'A'.