Question

why ice has low density ... therefore it is a solid

Answer 1

solid has a low density compare to any other solid because of its structure. ice has a cage like structure their are a lot of space inside it which is filled with gas the gas has lowest density therefore ice has a lowest density compare to any other solid................

Answer 2

Though ice is a solid it has low density
The reason is that due to the anomalous expansion of water the density of the water is least at 0-4 degrees centigrade
This is the reason why ice floats( at this moment the the density of ice is lesser than that of water because it is at 0 degrees)
Hope it helps...