The H−N−H bond angle in ammonia molecule is 107∘. Since, the repulsion between lone pair- lone pair and lone pair-bond pair is more than that between bond pair-bond pair. The repulsion in H2O is much greater than that in NH3 which results in contraction of bond angle from 109∘28′ to 104.5∘ in water while in NH3 contraction i.e. less is from 109∘ 28 ' to 107∘.