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

Explanation

The hybridisation state of carbon atoms in the given compounds and % s-character of the orbital containing C-H bond are as follows:

The acidic behaviour depends upon the % s-character of the orbital containing C-H bond. As the s-character increases, the electrons of C-H bond lie closer and closer to the carbon atom. This leads to an increase in the partial positive charge on H atom and hence the acidic character increases. Since in ethyne, the s-character is maximum (50%), it is most acidic. The acidic character of these compounds decreases in the following order : Ethyne > Benzene > Hexane.