Assertion : $\mathrm{HC} \equiv \mathrm{C}^{-}$is more stable than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$…
Assertion : $\mathrm{HC} \equiv \mathrm{C}^{-}$is more stable than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$.Reason : $\mathrm{HC} \equiv \mathrm{C}^{-}$has more s-character than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false.
Solution
$\mathrm{HC} \equiv \mathrm{C}^{-}$has $50 \%$ s-character and $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$has $33 \%$ s-character. Stability of carbanions increases with an increase in the s-character at the carbanion. So $\mathrm{HC} \equiv \mathrm{C}^{-}$is more stable than $\mathrm{H}_2 \mathrm{C}=\mathrm{CH}^{-}$.