Arrange benzene, $n$-hexane and ethyne in decreasing order of their acidic behaviour.

The decreasing order of acidic behaviour is ethyne $>$ benzene $>n$-hexane Because carbon in ethyne, benzene and $n$-hexane are $s p, s p^{2}$ and $s p^{3}$ hybridised respectively.

$\therefore$ The carbocation formed after the removal of ' $\mathrm{H}$ ' is more stable in $s p$ hybridised carbon atom because of high electronegativity due to more $s$-character.