The first member of the alkyne series is

The correct option is C

$\left({\mathrm{C}}_2{\mathrm{H}}_2\right)$

Step 1:

The compounds containing Carbon $\left(\mathrm{C}\right)$ atoms have multiple bonds between two Carbon-Carbon $(\mathrm{C}-\mathrm{C})$ atoms are called unsaturated hydrocarbons.

The multiple bonds are either double or triple bonds.

Step 2:

The explanation for the correct option:

Alkenes and alkynes contain double and triple bonds between Carbon-Carbon atoms respectively. So these are known as unsaturated hydrocarbons.

The general formula of alkynes is $\left({\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}\right)$.

The first member of the alkyne series is Ethyne $\left({\mathrm{C}}_2{\mathrm{H}}_2\right)$.

The explanation for the incorrect option:

Methane $\left({\mathrm{CH}}_4\right)$ is a saturated hydrocarbon because it contains only a single bond between Carbon and Hydrogen $\left(\mathrm{H}\right)$ atoms.

Ethene $\left({\mathrm{C}}_2{\mathrm{H}}_4\right)$ is an unsaturated hydrocarbon because it contains double bonds between two Carbon-Carbon atoms.

Propene $\left({\mathrm{C}}_3{\mathrm{H}}_6\right)$ is an unsaturated hydrocarbon because it contains double bonds between two Carbon-Carbon atoms.

Final answer:

Hence, option (C) is the correct option.