Why does a straw look broken viewed in a glass of water?

This is due to refraction of light

Explanation:

When a straw is placed in a glass it appears to be broken as a result of refraction of light on the air-water interface.

Since, the refractive index of water is more than that of glass.

Also, water is denser than air, which means light travels slower in water than in air.

Most importantly, When light travels from rarer to denser medium it bents towards the normal and deviates from its original path which explains the broken view of straw in a glass of water.