Question

Which pair of compounds are isomers?

(1) NO2 and N2O4
(2) P2O5 and P4O10
(3) HCOOH and CH3COOH
(4) CH3OCH3 and C2H5OH

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`

Step-by-step 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.