Question

why does ice float? as water freezes, air becomes trapped between the hydrogen bonds of water molecules. as water freezes, it expands and its density decreases. as water freezes, it takes up more hydrogen from the atmosphere, causing it to have a greater buoyancy. as water freezes, it takes up more oxygen from the atmosphere, causing it to have a greater buoyancy.

Explanation:

To determine why ice floats, we analyze the properties of water when it freezes. The key concept is density: an object floats if its density is less than the fluid it's in. When water freezes into ice, the water molecules form a crystalline structure with hydrogen bonds, which causes the ice to expand (take up more space) while the mass remains the same. Since density is mass divided by volume ($
ho = \frac{m}{V}$), an increase in volume (while mass is constant) leads to a decrease in density. So ice, with lower density than liquid water, floats.

Let's evaluate the options:

• Option 1: Trapping air between hydrogen bonds of water molecules is not the main reason for ice's lower density compared to liquid water. The structure of the ice lattice (due to hydrogen bonding) causes expansion, not just air trapping.
• Option 2: As water freezes, it expands (increases volume) and since density is inversely proportional to volume (for constant mass), its density decreases. This makes ice less dense than liquid water, so it floats. This matches the scientific explanation.
• Option 3: Taking up more hydrogen from the atmosphere is incorrect. The hydrogen in water molecules is already present in the water, and freezing doesn't involve taking in hydrogen from the atmosphere to affect buoyancy.
• Option 4: Taking up more oxygen from the atmosphere is also incorrect. Freezing water doesn't involve absorbing oxygen from the atmosphere to increase buoyancy. The change in density due to expansion (from the ice lattice structure) is the primary reason.

Answer:

The correct option is: "As water freezes, it expands and its density decreases." (The second option in the list of choices provided in the problem)