Among the following, the pair that is not a pair of metamers is

→ The structures which have same molecular formula but differ in nature and number alkyl chain on either side of bivalent functional group are called metamers and the phenomina is said to be metamerism

Examples:

→ The above two isomers differ in the position of –OCH₃ group hence, they are positional isomers but not metamers, since carbon chain lengths are same.