(a) Compounds having the same molecular formula but with different structures are

called structural isomers. The given compounds have the same molecular formula but they

differ in the position of the functional group (ketone group).

In structure I, ketone group is at the C-3 of the parent chain (hexane chain) and in

structure II, ketone group is at the C-2 of the parent chain (hexane chain). Hence, the

given pair represents structural isomers.

(b) Compounds having the same molecular formula, the same constitution, and the

sequence of covalent bonds, but with different relative position of their atoms in space are

called geometrical isomers.

In structures I and II, the relative position of Deuterium (D) and hydrogen (H) in space

are different. Hence, the given pairs represent geometrical isomers.

(c) The given structures are canonical structures or contributing structures. They are

hypothetical and individually do not represent any real molecule. Hence, the given pair

represents resonance structures, called resonance isomers.