Question

why ice have lower density than water​

Answer 1

Answer:

Ice has a lower density than water because of hydrogen bonding and cage-like structure of ice.

Ice has hexagonal three-dimensional crystal structure (as per X-ray crystallographic data). This hexagonal crystal structure is formed  due to intermolecular hydrogen bonding.

When ice melts, some of hydrogen bonds break and some empty spaces are occupied by water molecules. Liquid water molecules are more closely packed than molecules in ice. Hence, ice has lower density than water.

Explanation:

So, this is your answer