Answer:
The relationship between the given compound, (CH₃)₂CHCH(CH₃)CHO, and the options provided is that it is an aldehyde.
An aldehyde is a functional group in organic chemistry characterized by the presence of a carbonyl group (-C=O) bonded to at least one hydrogen atom and one carbon atom. In the given compound, the presence of the "-CHO" group indicates the presence of an aldehyde functional group. Hence, the correct choice is (a) Aldehyde.