Question

Ethene is known as the first member of the:
A.Unsaturated hydrocarbons
B.Alkyne series
C.Saturated hydrocarbons
D.Alkane series
E.Aromatic hydrocarbons.

Answer 1

Hydrocarbons are the chemical compounds that are categorized under organic chemistry. These compounds are composed of carbon and hydrogen atoms only via different frameworks of arrangements. Hydrocarbons are majorly classified into two types, saturated hydrocarbons and unsaturated hydrocarbons.

Complete answer:
Ethene is a colourless gas which has flammable properties. In its pure state, it has a sweet and musky odour. Its molecular formula is ${C_2}{H_4}$.
Now as per given options,
Unsaturated hydrocarbons are the types of hydrocarbons which consist of a double or triple bond within the molecules. On the basis of types of bond present, it is divided into two types:
Alkenes: The unsaturated compounds which consist of a double bond are termed as alkenes. The general formula of alkenes is ${C_n}{H_{2n}}$. The first member of the alkene family or series is ethene with a molecular formula of ${C_2}{H_4}$.
Alkynes: The unsaturated compounds which consist of a triple bond are termed as alkynes. The general formula of alkynes is ${C_n}{H_{2n - 2}}$. The first member of the alkyne family is ethyne with a molecular formula of ${C_2}{H_2}$.
Saturated hydrocarbons: These are the types of hydrocarbons which consist of only sigma bonds or single bonds between the carbon atoms within a molecule. These are alternatively termed as alkanes. The general formula of alkanes is ${C_n}{H_{2n + 2}}$. The first member of the alkane series is methane with a molecular formula of $C{H_4}$.
Aromatic hydrocarbons are a special type of unsaturated hydrocarbons which are planar cyclic structures consisting of a conjugated system of $\pi$ bonding and follows Huckel’s rule. Example for aromatic hydrocarbons is benzene, toluene, etc.
Hence, it can be concluded that ethene is known as the first member of the unsaturated hydrocarbons.

Thus, option (A) is the correct answer.

Note:
Hybridization of the carbon atom varies with the type of bonding present in the molecule. In ethene, it consists of a double bond between two carbon atoms, so hybridization for both the hydrocarbons is $s{p^2}$.