The correct option is
D 3- methylbut-2-enoic acid
CH3−CH3|C=CH−COOH
4 3 2 1
The IUPAC name of the given compound is 3-methylbut-2-enoic acid.
The longest continuous chain contains 4 C atoms so it is considered as a derivative of butane.
A C=C double bond is present between the second and third C atom.
Hence, butane is replaced with 2-butene. A carboxylic group (-COOH) is present on the first C atom. Hence, 2-butene is replaced with 2 - butenoic acid.
A methyl substituent is present on third C atom which is named as a prefix.
Option C is correct.