Carbonyl group IR absorption Steps:

• The 1610–1750 cm⁻¹ range indicates strong C=O stretching vibration in carbonyl compounds.
• Identify functional groups from molecular formulas, ensuring no cyclic structures.
• P (CH₄O): Possible structure is CH₃OH (methanol), an alcohol with O–H but no C=O.
• Q (CH₂O): Structure is H₂C=O (formaldehyde), an aldehyde with C=O.
• R (C₂H₄O): Structure is CH₃CHO (acetaldehyde), an aldehyde with C=O. Why C is correct:
• Q and R contain carbonyl groups, which produce strong C=O absorption per IR spectroscopy principles for C=O stretch. Why the others are wrong:
• A: Excludes R, but R has a carbonyl.
• B: Excludes Q, but Q has a carbonyl.
• D: Includes P, but P lacks a carbonyl.

Final answer: C