1. Principle for nucleophilic addition to carbonyl compounds

   The reactivity of aldehydes and ketones towards nucleophilic addition depends mainly on:

   • Electronic effect: Greater positive charge on the carbonyl carbon increases reactivity.
   • Steric effect: Less hindrance around the carbonyl carbon increases reactivity.

2. Aldehydes vs ketones

   Aldehydes are generally more reactive than ketones because:

   • They have only one alkyl/aryl group and one hydrogen, so less steric hindrance.
   • Ketones have two carbon-containing groups, which reduce electrophilicity and increase steric hindrance.

   Therefore, $\text{acetophenone} < \text{aromatic aldehydes}$

3. Compare the aromatic aldehydes

   We now compare:

   • benzaldehyde
   • $p$-tolualdehyde
   • $p$-nitrobenzaldehyde

   In aromatic aldehydes, substituents on the benzene ring affect the electrophilicity of the carbonyl carbon.

   (i) $p$-Tolualdehyde

   The $p$-methyl group is electron-donating due to its $+I$ effect and hyperconjugation. It decreases the positive character on the carbonyl carbon, so it makes nucleophilic addition slower than in benzaldehyde.

   Hence, $p\text{-tolualdehyde} < \text{benzaldehyde}$

   (ii) $p$-Nitrobenzaldehyde

   The $p$-nitro group is strongly electron-withdrawing by both $-I$ and $-M$ effects. It increases the positive character on the carbonyl carbon, so it makes nucleophilic addition faster than in benzaldehyde.

   Hence, $\text{benzaldehyde} < p\text{-nitrobenzaldehyde}$

4. Overall order

   Combining all comparisons: $\text{acetophenone} < p\text{-tolualdehyde} < \text{benzaldehyde} < p\text{-nitrobenzaldehyde}$

5. Check options

   • A: acetophenone $<$ benzaldehyde $<$ $p$-tolualdehyde $<$ $p$-nitrobenzaldehyde ❌
   • B: acetophenone $<$ $p$-tolualdehyde $<$ benzaldehyde $<$ $p$-nitrobenzaldehyde ✅
   • C: reverse order ❌
   • D: incorrect placement of acetophenone and $p$-tolualdehyde ❌

Therefore, the correct option is B.