Q.Nitromethane condenses with acetaldehyde to give :

Nitromethane's $\alpha$-hydrogens (on the carbon bearing $-NO_2$) are acidic because the resulting carbanion is stabilised by the strongly electron-withdrawing nitro group. Under mild base, this carbanion undergoes a nitroaldol (Henry) condensation, attacking the electrophilic carbonyl carbon of acetaldehyde.

Mechanism: $^-CH_2NO_2$ (from $CH_3NO_2$) attacks $CH_3CHO$'s carbonyl carbon, giving the alkoxide $CH_3-CH(O^-)-CH_2NO_2$, which is protonated to $CH_3-CH(OH)-CH_2NO_2$. Numbering this propanol chain from the nitro-bearing end: C1 = $CH_2NO_2$, C2 = $CH(OH)$, C3 = $CH_3$ — giving 1-nitropropan-2-ol, i.e. 1-nitro-2-propanol. Option (a), 2-nitro-1-propanol, places the substituents on the wrong carbons (woul …