regularly dissolve in water:\n20. what allows solid water (ice) to be less dense than liquid water?\n21. how…

Explanation:

Step1: Explain ice density

Ice has a less - dense structure than liquid water because of hydrogen bonding. In ice, water molecules form a regular hexagonal lattice due to hydrogen bonds. The open - lattice structure creates more space between molecules compared to the more closely packed arrangement in liquid water, making ice less dense.

Step2: Explain ice's role for life under water

The fact that ice floats on water (due to its lower density) creates an insulating layer on the surface of a lake. This layer of ice reduces heat loss from the water below to the cold air above. As a result, the water beneath the ice remains at a relatively stable and warmer temperature (around 4°C, which is the temperature at which water has its maximum density), allowing aquatic life to survive during cold periods.

Answer:

20. Hydrogen bonding causes water molecules in ice to form a more open hexagonal lattice structure, increasing the space between molecules and making ice less dense than liquid water.
21. The floating ice on a lake surface acts as an insulating layer, reducing heat loss from the water below and maintaining a relatively stable and warmer temperature in the water, allowing life to continue.