Priority order is very important in nomenclature.
If \(-\text{COOH}\) and \(-\text{CHO}\) are both present, choose \(-\text{COOH}\) as the principal functional group.
Concept:
When a benzene ring contains both \(-\text{COOH}\) and \(-\text{CHO}\) groups, the carboxylic acid group has higher priority than the aldehyde group.
So the parent name is based on benzoic acid, and the aldehyde group is written as the substituent formyl.
ip
Step 1: Identify the principal functional group.
Among the groups present, \(-\text{COOH}\) has higher priority than \(-\text{CHO}\).
Therefore, the parent compound is:
\[
\text{benzoic acid}
\]
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Step 2: Number the benzene ring starting from the carboxylic acid carbon.
Numbering starts from the carbon attached to \(-\text{COOH}\), which is carbon 1.
Then we assign numbers to substituents so that the set of locants is minimum.
From the given structure:
• the formyl group comes at position 3,
• the methyl group comes at position 6
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Step 3: Write the name in correct format.
So the correct IUPAC name is:
\[
\text{3-Formyl-6-methylbenzoic acid}
\]
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Hence, the correct answer is:
\[
\boxed{(C)\ \text{3-Formyl-6-methylbenzoic acid}}
\]
