To understand how water (H₂O) molecules differ from most other molecules, we need to look at the behavior of water when it is cooled.
Most substances contract when they cool because the molecules move closer together as their thermal energy decreases. However, water is quite unique in this regard.
When water is cooled from room temperature, it behaves normally up to 4°C, contracting as expected. But as it cools further from 4°C to 0°C, it starts expanding instead of continuing to contract. This is due to the hydrogen bonding interactions between water molecules; as the temperature decreases, these bonds arrange the water molecules into a hexagonal lattice that takes up more space than in the liquid state. This arrangement is why ice is less dense than liquid water and floats.
The correct way water molecules differ from most other molecules is:
C. They expand when cooled to [tex]$0^{\circ} C$[/tex].
