Ans) To understand why ice floats, one must first grasp the concept of density. Density is calculated by dividing an object's mass (the amount of matter it contains) by its volume (the amount of space it takes up), or D=M/V. Density essentially describes how tightly packed the atoms of a substance are. The atoms in a high-density substance are tightly packed, whereas the atoms in a low-density substance are more spread out. Density is a defining property of a substance, and it remains constant regardless of how much of the substance is present. The density of pure liquid water is 1.0 g/mL, and it serves as a standard against which other substances are measured.When water freezes, the water molecules spread out and align to form a distinct crystalline structure.   Water expands as it solidifies, whereas most other substances contract.Because water expands when it freezes, ice occupies more space (has a larger volume) than liquid water. However, the amount of matter has not changed; it has simply been spread out over a larger area. This means that ice has a lower density (0.92 g/mL) than liquid water (1.0 g/mL). Ice floats in water because its density is lower than that of water.