IR spectrum identifies aldehyde via characteristic C-H stretch Steps:

• Examine IR for carbonyl region (~1700 cm⁻¹) to confirm C=O presence in all options.
• Look for aldehyde-specific C-H stretches at 2720 and 2820 cm⁻¹, indicating CHO group.
• Check absence of broad O-H stretch (~3000 cm⁻¹) to rule out carboxylic acid.
• Verify no other unique peaks like those for ketones alone.

Why C is correct:

• Butanal (CH₃CH₂CH₂CHO) shows twin C-H stretches at 2720–2820 cm⁻¹ due to aldehydic hydrogen, per IR correlation tables.

Why the others are wrong:

• A and B (both butan-2-one): Ketone C=O at ~1715 cm⁻¹ but lacks aldehydic C-H peaks.
• D (butanoic acid): Broad O-H stretch at 2500–3300 cm⁻¹ from carboxylic acid dimerization.

Final answer: C