Explanation

(b)
In ethanol the oxygen of $–OH$ group is bonded to the $sp^{3}$ hybridised carbon by a sigma bond. The $C - O - H$ bond angle in ethanol is less than the tetrahedral angle $(109{^\circ},\ 28^{''})$ due to larger repulsions between the lone pair of repulsions between the lone pairs of oxygen. Hence, it is $104{^\circ}$ in ethanol.
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