Which of the following types of water is the most dense?

• A. Liquid water at 25 ^ext{o}C
• B. Liquid water at 4 ^ext{o}C
• C. Water vapor at 100 ^ext{o}C
• D. Ice at 0 ^ext{o}C

Answer: (B)

Verified step by step guidance

1. Recall that the density of a substance is defined as its mass per unit volume, given by the formula \(\text{density} = \frac{\text{mass}}{\text{volume}}\).
2. Understand that water exhibits an unusual property: its density varies with temperature, and it reaches a maximum density at approximately 4 \(^\{\circ\}\)C.
3. Compare the states of water given: liquid water at 25 \(^\{\circ\}\)C, liquid water at 4 \(^\{\circ\}\)C, water vapor at 100 \(^\{\circ\}\)C, and ice at 0 \(^\{\circ\}\)C. Note that gases (water vapor) generally have much lower densities than liquids or solids.
4. Recognize that ice (solid water) is less dense than liquid water, which is why ice floats on water. Also, liquid water at 25 \(^\{\circ\}\)C is less dense than at 4 \(^\{\circ\}\)C due to thermal expansion.
5. Conclude that among the options, liquid water at 4 \(^\{\circ\}\)C has the highest density because it is the temperature at which water molecules are most closely packed.