Final answer:
Water's lower density in its solid form (ice) allows it to float on liquid water, which is important for the survival of aquatic organisms. which is why lakes and ponds freeze from the top down. If ice were denser than liquid water, it would sink, causing entire lakes to freeze solid, making it impossible for aquatic organisms to survive in the water beneath the ice.
Step-by-step explanation:
Water has a lower density in its solid form (ice) because of the way hydrogen bonds orient as they freeze. The water molecules push farther apart in ice compared to liquid water. This is due to the expansion that happens when water freezes, causing the ice to have a lower density than the liquid water.
This lower density of ice compared to liquid water has important consequences. Ice floats on the surface of liquid water, which is why lakes and ponds freeze from the top down. If ice were denser than liquid water, it would sink, causing entire lakes to freeze solid, making it impossible for aquatic organisms to survive in the water beneath the ice.