Question

Which formula represents an unsaturated
organic compound?
(1) CH4 (3) C3H8
(2) C2H4 (4) C4H10

Answer 1

The only saturated hydrocarbons are Alkanes:   $C_{n} H_{2n+2}$

From that we can see that:
CH4, C3H8 and C4H10  are saturated.

Therefore:
C2H4   is unsaturated.   Answer is (2).

Answer 2

Answer: (2) $C_2H_4$

Explanation: Unsaturated organic compounds are those compounds which contains carbon-carbon double or triple bond.

Saturated organic compounds are those compounds which contains carbon-carbon single bond.

$CH_4$, $C_3H_8$ and $C_4H_10$ are all alkanes having general formula $C_nH_{2n+2}$ containing single bonds.

$C_2H_4$ is an alkene having general formula $C_nH_{2n}$ containing double bonds.