Snowflakes begin to form when water in the atmosphere freezes it causes the water molecules to bond into a hexagonal shape. Is this sentence correct?

Yes! This sentence is correct.

Explanation:

So the complete question along with options is:

Q. Snowflakes begin to form when water in the atmosphere freezes it causes the water molecules to bond into a hexagonal shape.

a) no change

b) freezes, causing

c) freezes, it causes

d) freezes, this causes.

The coorect option is c.