Which of the following is an alkyl group? 

An alkyl group is formed by removing a hydrogen atom from an alkane molecule. Alkanes are quite often represented as R-H, where R stands for an alkyl group. The general formula of an alkyl group is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}+1}.$ The smallest alkyl group is ${\mathrm{CH}}_3$ called methyl which is obtained by removing one hydrogen from methane.

The alkyl group next to methyl is the ethyl group with two carbon atoms. It is represented as-

$-{\mathrm{CH}}_2{\mathrm{CH}}_3$.

• Ethane is an alkane and not an alkyl group.
• Ethyne is an alkyne ( having a triple bond) and it not an alkyl group.

Thus, the correct option is (A).