Question

An unsaturated hydrocarbon :

• A. contains only six carbon atoms.
• B. contains fewer hydrogen atoms than is needed for carbon to have its usual valency of four.
• C. Always contains equal number of carbon and hydrogen atoms.
• D. Contains a chain of carbon and oxygen atoms.

Answer 1

The correct option is B contains fewer hydrogen atoms than is needed for carbon to have its usual valency of four.

Unsaturated hydrocarbons have double or triple bonds present in the carbon chain. So, these carbon atoms with double or triple bonds have fewer hydrogen atoms as the valency of carbon is already being satisfied by the extra bonds between the carbon atoms.

Also, unsaturated hydrogen carbons can have any number of carbon atoms in its chain. Additionally, a hydrocarbon is always made of carbon and hydrogen atoms, it has no other atoms in its structure.

Hence, option $B$ is correct.