Question

Write general formula of Alkene:
A. \[{C_n}{H_{2n}}\]
B. \[{C_n}{H_{2n + 2}}\]
C. \[{C_n}{H_{2n - 2}}\]
D. \[{C_n}{H_n}\]

Answer 1

Hint:Alkenes are a class of hydrocarbon that contains a carbon-carbon double bond. Alkenes are called unsaturated hydrocarbons because they have fewer hydrogen atoms than does an alkane with the same number of carbon atoms.

Complete answer:
Alkenes are hydrocarbons with carbon-to-carbon double bonds \[\left( {{R_2}C = C{R_2}} \right)\] .
The alkenes form a homologous series. Like all homologous series, the alkenes have the same general formula. The general formula for the alkenes is \[{C_n}{H_{2n}}\] , where n is the number of carbon atoms in the molecule.
For example: Ethene is an alkene. Its molecules contain 2 carbon atoms and the molecular formula of ethene is \[{C_2}{H_4}\] . This is because $n = 10$ . So, $2n = 2 \times 2 = 4$ .
The double bond is shared by the two carbons and does not involve the hydrogen atoms, although the condensed formula does not make this point obvious. The structure of ethene is
${H_2}C = C{H_2}$
The alkenes are unsaturated hydrocarbons because they are compounds containing hydrogen and carbon only, unsaturated, because they contain a \[C = C\] double bond, which means that they have two fewer hydrogen atoms than the corresponding alkane. The \[C = C\] bond is the functional group in the alkenes. It is responsible for the typical reactions of alkenes.
Hence, the general formula of alkenes is \[{C_n}{H_{2n}}\] , where n is the no. of carbon atoms.

Therefore. The correct answer is option (A).

Note:
Just like the alkanes, the alkenes undergo combustion. However, they are less likely to combust completely, so they tend to burn in air with a smoky flame due to incomplete combustion.