Explanation

(d)
An organic ion with a pair of available electrons and a negative charge on the central carbon atom is called a carbanion.
Electron attracting group [image:12_image287.emf]increases stability and electron releasing group $( - CH_{3}etc)$ decreases the stability of carbanion. In $\left( CH_{3} \right)_{3}C^{-}$, three $–CH_{3}$ groups (electron releasing group) are present, so it least stable.