HgCl2 is 180 degrees.

H2O is 104.5 degrees.

PH3 is 90 degrees.

Mercury chloride is a special case and the other three are hydrides of different elements. When they compare, they need to look at the electronegativity of the central atom. Compared with PH3, the greater the electronegativity of ammonia gas, the greater its attraction to lone pair, while both lone pair and chemical bond (here, valence bond electron pair) are negatively charged, which will lead to a larger bond angle. When ammonia is compared with water, the bond angle of water is smaller than that of ammonia, because ammonia has a pair of solitary pairs and water has two pairs. The mutual repulsion of two pairs of solitary pairs in water will make the repulsion between two O-H bonds squeeze inward much more than that between electron pairs of * * * *.