Arrange the following compounds in increasing order of their reactivi…

The correct answer is Option (1) → D, C, B, A

Alkyl groups lower the reactivity of the C=O carbon by both an electronic (+I) and a steric effect, so aldehydes are more reactive than ketones.

Both factors act in the same direction, so aldehydes are more reactive than ketones, and within each class the compound with smaller alkyl groups is more reactive:

    \( \displaystyle \text{ketone (larger groups)} < \text{ketone} < \text{aldehyde (larger group)} < \text{aldehyde} \)

    \( \displaystyle \ce{CH3COCH2CH3} < \ce{CH3COCH3} < \ce{CH3CH2CHO} < \ce{CH3CHO} \)

Matching the given compounds:

• D. Butanone: \( \ce{CH3COCH2CH3} \) (ketone, \( \ce{CH3} \) and \( \ce{C2H5} \))

• C. Propanone: \( \ce{CH3COCH3} \) (ketone, two \( \ce{CH3} \))

• B. Propanal: \( \ce{CH3CH2CHO} \) (aldehyde, \( \ce{C2H5} \))

• A. Ethanal: \( \ce{CH3CHO} \) (aldehyde, \( \ce{CH3} \))

Shortcut: Butanone (D) is the least reactive and ethanal (A) the most reactive. Only Option (1) starts with D and ends with A.

NCERT (2026-27 edition):
Reactivity

Note: The same/similar question has been asked in different years by NTA as per the details given below: