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Question

# A hydrocarbon has $4$ hydrogen atoms. Give its molecular formula if its alkyne.

A

CH4

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B

C3H4

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C

C2H6

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D

C2H4

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Solution

## The correct option is B ${\mathrm{C}}_{3}{\mathrm{H}}_{4}$Explanation for correct option:(B) ${\mathrm{C}}_{3}{\mathrm{H}}_{4}$An alkyne is an unsaturated hydrocarbon that contains at least one C-C triple bond.The general formula for alkynes is specified as ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2\mathrm{n}-2}$. Here, $\mathrm{n}$ represents the number of carbon atoms.The number of hydrogen atoms for the molecular formula is 4.The number of the carbon atoms can be calculated as follows: $2\text{n}-2=4\phantom{\rule{0ex}{0ex}}\text{n}=3$So, the number of carbon atoms in the molecular formula is 3. Hence, the molecular formula of alkyne will be ${\mathrm{C}}_{3}{\mathrm{H}}_{4}$.Explanation for incorrect options:(A) Methane $\left({\mathrm{CH}}_{4}\right)$ is a saturated hydrocarbon and it does not have any C-C triple bond thus, it is an alkane not alkyne.(C) Ethane $\left({\mathrm{C}}_{2}{\mathrm{H}}_{6}\right)$ has C-C single bond thus, it is an alkane not alkyne.(D) Ethene $\left({\mathrm{C}}_{2}{\mathrm{H}}_{4}\right)$ is an unsaturated hydrocarbon and it has one C-C double bond thus, it is an alkene not alkyne.Hence, the correct option is (B) i.e. ${\mathrm{C}}_{3}{\mathrm{H}}_{4}$.

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