Butanone, $\text{CH}_3\text{CH}_2\text{COCH}_3$, together with HCN and a small amount of KCN, undergo a nucleophilic addition reaction. Which statement correctly describes the mechanism of this nucleophilic addition reaction?
- AThe $\pi$ bond pair of $\text{C{=}O}$ accepts $\text{H}^+$ from HCN and then $\text{CN}^-$ acts as a nucleophile.
- BA $\pi$ bond pair from $\text{CN}^-$ attacks the $\delta^+$ C and HCN then donates $\text{H}^+$ to O.
- CThe lone pair on O accepts $\text{H}^+$ from HCN and then $\text{CN}^-$ acts as a nucleophile.
- DA lone pair from $\text{CN}^-$ attacks the $\delta^+$ C and then $\text{O}^-$ accepts $\text{H}^+$ from HCN.