Aldehydes are more reactive than ketones towards nucleophilic addition.

Solution

Chemistry ma’am · 4 steps

Look at what sits next to the carbonyl carbon: one H in an aldehyde, two R groups in a ketone.

1. Electronic effect. Alkyl groups push electron density towards the carbonyl carbon by their +I effect. A ketone has two alkyl groups, an aldehyde has only one, so the carbonyl carbon of an aldehyde stays more positive and attracts a nucleophile more strongly.
2. Steric effect. The nucleophile must reach the carbonyl carbon, which changes from flat sp² to crowded sp³ in the product. A small H atom gets in the way far less than a second bulky alkyl group, so the attack and the product are both easier for an aldehyde.
3. An example. Methanal (HCHO) is more reactive than ethanal (CH₃CHO), which is more reactive than propanone (CH₃COCH₃). Each extra alkyl group lowers the reactivity.
4. So. Both effects point the same way, so aldehydes are more reactive than ketones towards nucleophilic addition. The statement is true.

The idea to keep. For nucleophilic addition, ask two questions: how positive is the carbonyl carbon, and how crowded is it? Fewer alkyl groups means more positive and less crowded, so it reacts faster.

Answer from the NTA final answer key. Solution by PrepWiser.