Ethoxy ethane and Methoxy propane are

Isomers having bivalent groups −C||O−,−C||O−O−,−NH−,−O− and different alkyl groups on its either side, are called metamers.CH3−CH2−O−CH2−CH3 (Ethoxy ethane)and CH3−O−CH2CH2−CH3  (Methoxy propane)are having bivalent group –O-.Hence, option (3) metamers is correct.