Answer:
Propanoic acid. Option D is correct
Explanations:
The functional group of the compound is R-COOH where the R group are the methyl groups
From the given compound CH3CH₂COOH, the R-group which is CH3CH2C is "propane (3-carbon chain)". Since the suffix for carboxylic acid is -oic, hence the name of the compound is propanoic acid