Question

${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n}}}}$ is the general formulae of ___________.
a) Alkene
b) Alkane
c) Alkyne
d) Alcohol

Answer 1

Hint: Alkane is a saturated compound while alkene and alkyne are unsaturated hydrocarbons. If unsaturation is present in a hydrocarbon, the number of hydrogen will be less.

Complete step by step answer:
A general formula helps us to write the molecular formula of a hydrocarbon. From the general formula ${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n}}}}$, it is clear that number of hydrogen will be double of the number of carbons. Let us take the number of carbon is two. Then the number of hydrogen will be 4. So, the molecular formula will be ${\text{C}}{{\text{H}}_{\text{2}}}{\text{ = C}}{{\text{H}}_{\text{2}}}$. There is a double bond in the compound. Therefore, the general formula ${{\text{C}}_{\text{n}}}{{\text{H}}_{{\text{2n}}}}$ is of alkene.
So, the correct option is (a).

Additional Information:
1.) Alkanes is also known as paraffin is a hydrocarbon which is acyclic and saturated. All the carbon-carbon bonds are single in alkanes.
2.) At least one carbon-carbon double bond is present in alkene which is an unsaturated hydrocarbon. Alkenes can be named as alkadienes, alkatrienes, alkatetraenes, etc. according to their number of double bonds present in them.
3.) At least one carbon-carbon triple bond is present in alkynes which is also an unsaturated hydrocarbon.

Note: Alcohol is not the correct option for this question because alcohol is the hydrocarbon derivative that contains an –OH group. There is no oxygen in the general formula. Please note that, in the general formulas of alcohols, aldehyde, ketones and carboxylic acids, there is at least one oxygen present.