Write the general formula of Alkene:

Unsaturated hydrocarbons (carbon-hydrogen compounds) are those hydrocarbons that have two or three double or triple covalent bonds between their surrounding carbon atoms. Alkene molecules have double bonds, hence they are categorised as unsaturated hydrocarbons.

Alkenes are unsaturated hydrocarbons containing at least one double bond between carbon atoms. Alkenes are sometimes referred to as olefins. Alkenes have more reactive properties than alkanes because they include a double bond.
We need to look at a few instances of these compounds in order to identify the common pattern that underlies all of these compounds before we can assign them a generic formula.
Alkene examples include the following:

(Apiece carbon should meet the requirement that they contain four hydrogen atoms each.)

${\mathrm{CH}}_2={\mathrm{CH}}_2,{\mathrm{CH}}_3-\mathrm{CH}={\mathrm{CH}}_2,{\mathrm{CH}}_3-\mathrm{CH}=\mathrm{CH}-{\mathrm{CH}}_3$

We can see that there are four hydrogen atoms present when there are two carbon atoms, six hydrogen atoms when there are three carbon atoms, and eight hydrogen atoms when there are four carbon atoms.
After thorough examination, we discover that there will be twice as many hydrogen atoms as carbon atoms in the final product. Therefore, there should be twice as many hydrogen atoms in the formula as there are carbon atoms.
Consequently, the generic formula may be expressed as follows:

For $n$ given carbon atoms, there will be alkenes with formula $\Rightarrow C_n{H}_{2n}$
Therefore the general formula is $C_n{H}_{2n}$ .

Hence, the correct option is A.