IUPAC name of isobutyraldehyde is

The correct answer is Option (2) → 2-methylpropanal.

The common name of an aldehyde comes from the carboxylic acid it gives on oxidation. The IUPAC name takes the longest chain that contains the –CHO group, numbers the CHO carbon as C1 and ends in “-al”. Isobutyraldehyde is \( \ce{(CH3)2CH-CHO} \): its longest chain through the CHO carbon has three carbon atoms (propanal), with a methyl group on C2:

    \( \displaystyle \ce{CH3-CH(CH3)-CHO} \)

So its IUPAC name is 2-methylpropanal.

NCERT (2026-27 edition):
Nomenclature – …