Question
Arrange ethyne, ethene and ethane in the order of increasing acidity.

Answer

In alkynes, due to higher electonegativity of 'sp' hybridised carbon, which is due to $50 \% \mathrm{~s}$-character, the hydrogen atom is less tightly held by the carbon and hence $\left(\mathrm{H}^{+}\right)$can be removed by a strong base. Therefore, alkynes are most acidic and alkanes are least.
$\text{CH}_3-\text{CH}_3<\text{CH}_2=\text{CH}_2<\text{HC}\equiv\text{CH}$ is increasing order of acidity.

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