${\mathrm{CH}}_3{\mathrm{COCH}}_3$ and ${\mathrm{CH}}_2=\mathrm{COH}-{\mathrm{CH}}_3$ represents

Aldehydes and ketones have the carbonyl group in their structure, then you have already memorized a fact which would help you to differentiate between both of them.

Aldehydes and ketones are two different yet similar organic compounds, they are often confused due to their exceptions in generalities.CH₃COCH₃ is aldehyde and CH₂=COH–CH₃ is ketone, thus they are Functional isomers.