Question

Which pair of compounds are isomers?

Answer 1

CH3OCH3 and C2H5OH are isomers. They have same molecular formula. But with another formation. 

Answer 2

Answer: $CH_3OCH_3$ and $C_2H_5OH$

Explanation: The compounds having similar molecular formula but different arrangement of atoms or groups in space are called isomers and the phenomenon is called as isomerism.

$CH_3OCH_3$ and $C_2H_5OH$ are functional isomers which have same molecular formula but different functional groups attached.

(1) $NO_2$ and $N_2O_4$ are different compounds.

(2)  $P_2O_5$ and $P_4O_{10}$ are different compounds.

(3) $HCOOH$ and $CH_3COOH$ are different compounds.