Enumerating ester isomers for C4H8O2

Steps:

• Esters have structure RCOOR', with total C atoms in R + R' = 3 for C4H8O2.
• Formate esters (R = H): pair with propanol isomers—n-propyl formate (HCOOCH2CH2CH3) and isopropyl formate (HCOOCH(CH3)2).
• Acetate esters (R = CH3): pair with ethanol—ethyl acetate (CH3COOCH2CH3).
• Propanoate esters (R = CH3CH2): pair with methanol—methyl propanoate (CH3CH2COOCH3).
• No other combinations fit, as longer acids require fewer carbons in R' than possible.

Why C is correct:

• Four isomers match the formula per structural isomerism in organic nomenclature.

Why the others are wrong:

• A: Underestimates by ignoring formate and branched options.
• B: Misses one formate isomer.
• D: Overcounts, as no valid fifth ester exists.

Final answer: C