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

Explanation

The decreasing order of acidic behaviour is ethyne`gt`benzene`gt`n-hexane.
The C-H bonds in ethyne, benzene and hexane are formed by `sp-s,sp^(2)-s and sp^(3)-s` overlap reaspectively.
Since sp hybridized carbon is more electronegative then `sp^(2)` hybridized carbon which in turn is more electronegative than `sp^(3)`-hybridized carbon, therefore, the polarity of C-H bond is in the order.
Ethyne `gt` benzene `gt` hexane
Consequently, the acidity is in the order :
Ethyne `gt` benzene `gt` hexane