Arrange benzene, n-hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.

Acidic character of a species is defined on the basis of ease with which it can lose its H–atoms.

The hybridization state of carbon in the given compound is:

As the s–character increases, the electronegativity of carbon increases and the electrons of C–H bond pair lie closer to the carbon atom. As a result, partial positive charge of H–atom increases and H⁺ ions are set free.

The s–character increases in the order:

sp³ < sp² < sp

Hence, the decreasing order of acidic behaviour is Ethyne > Benzene > Hexane.