system
Given the following post, respond as if you're commenting on Reddit:
human
Why does water freeze clear after it's boiled?

I was just wondering why when you freeze water it is cloudy. But when you boil it, it freezes crystal clear?
gpt
The 'cloudiness' comes from oxygen which is in solution in the water.  When there's oxygen in water as it freezes, ice crystals can nucleate in many, many places which leads to polycrystalinity and you get some diffuse scattering of light through the ice.  When you boil water, most of the dissolved oxygen is expelled.