In the benzoin condensation catalysed by cyanide, the key role of $CN X^{-}$ is

Ato add to the carbonyl carbon and give a carbanion stabilised by $CN$ and phenyl, which attacks a second benzaldehyde
Bto remove an alpha-hydrogen of benzaldehyde and form an enolate
Cto donate a hydride ion to a second benzaldehyde, as in Cannizzaro reaction
Dto protonate the carbonyl oxygen, making it more electrophilic

Answer: A

Benzaldehyde has no alpha-hydrogen. Cyanide adds to the C=O and the resulting cyanohydrin anion transfers its C-H proton, giving a carbanion stabilised by

CN

and phenyl. This carbanion (polarity reversal) acts as nucleophile toward another benzaldehyde, and loss of

CN X^{-}

gives benzoin.

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In the benzoin condensation catalysed by cyanide, the key role of CNX− is

Answer: A

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In the benzoin condensation catalysed by cyanide, the key role of $CN X^{-}$ is