Concept:

Water exhibits anomalous expansion. Its density is maximum at \( 4^\circ\text{C} \) and it expands when freezing into ice at \( 0^\circ\text{C} \), making ice less dense than liquid water.

Formula:

$$ \text{Density} = \frac{\text{Mass}}{\text{Volume}} $$

Solution:

• At \( 0^\circ\text{C} \), water freezes into a rigid, open hexagonal lattice due to hydrogen bonding, creating empty spaces.



• Because volume increases by about 9%, the density of ice at \( 0^\circ\text{C} \) is less than the density of liquid water at the same temperature.

Why other options are incorrect:

Water has its maximum density at \( 4^\circ\text{C} \). At negative temperatures (like \( -4^\circ\text{C} \)), the substance is strictly solid ice, but the phase transition emphasizing the difference in density strictly occurs as it transitions around \( 0^\circ\text{C} \).