Question

The molecular formula of ethyne is __________.

• A. ${\mathrm{C}}_3{\mathrm{H}}_6$
• B. ${\mathrm{C}}_2{\mathrm{H}}_4$
• C. ${\mathrm{C}}_2{\mathrm{H}}_2$
• D. ${\mathrm{C}}_2{\mathrm{H}}_6$

Answer 1

The correct option is C

${\mathrm{C}}_2{\mathrm{H}}_2$

Explanation for correct option

(C)${\mathrm{C}}_2{\mathrm{H}}_2$

Alkynes

• Alkynes are also unsaturated hydrocarbons.
• They contain at least one triple bond between two carbon atoms.
• Unsaturated hydrocarbons contain carbon-carbon multiple bonds – double bonds, triple bonds or both.
• Saturated hydrocarbons contain carbon-carbon and carbon-hydrogen single bonds.
• The general formula of alkynes is ${\text{C}}_{\text{n}}{\text{H}}_{\text{2n–2}}$.
• Here, n is the number of carbon atoms in the molecule.

Ethyne

• An unsaturated hydrocarbons containing at least one carbon-carbon triple bond forms alkyne series.
• Ethyne is a simplest alkyne, which is a colourless gas.
• The compound is used as a fuel and a chemical building block.
• For example, ethyne contains two carbon atoms. So, the formula of ethyne is ${\mathrm{C}}_2{\mathrm{H}}_2$.
• Hence molecular formula of ethyne is${\mathrm{C}}_2{\mathrm{H}}_2$.

Explanation for incorrect option

• ${\mathrm{C}}_3{\mathrm{H}}_6$ is the molecular formula of propene. This molecule has three carbon atoms and six hydrogen atoms with one double bond.
• ${\mathrm{C}}_2{\mathrm{H}}_4$ is the molecular formula of ethene. This molecule has two carbon atoms and four hydrogen atoms with one double bond. .
• ${\mathrm{C}}_2{\mathrm{H}}_6$ is the molecular formula of ethane. This molecule has two carbon atoms and six hydrogen atoms with all single bonds.
• Hence, options (A), (B),and (D) are incorrect.

Hence, option (C) is correct. The molecular formula of ethyne is ${\mathrm{C}}_2{\mathrm{H}}_2$.