Which of the following must occur for solid water (ice) to change to liquid water?

• A. The temperature must decrease below 0^ext{o}C at 1 atm pressure.
• B. The temperature must increase above 0^ext{o}C at 1 atm pressure.
• C. The pressure must decrease below 1 atm while keeping the temperature constant at -10^ext{o}C.
• D. The pressure must increase above 1 atm while keeping the temperature constant at -10^ext{o}C.

Answer: (B)

Verified step by step guidance

1. Understand the phase change process for water from solid (ice) to liquid. This transition is called melting or fusion.
2. Recall that at 1 atm pressure, the melting point of ice is 0^\text{o}C. To change ice into liquid water, the temperature must reach or exceed this melting point.
3. Recognize that decreasing temperature below 0^\text{o}C will keep water in the solid phase, so this does not cause melting.
4. Consider the effect of pressure: at temperatures well below 0^\text{o}C (like -10^\text{o}C), changing pressure alone (either increasing or decreasing) will not cause ice to melt because the temperature is still below the melting point at 1 atm.
5. Therefore, the necessary condition for ice to melt at 1 atm is that the temperature must increase above 0^\text{o}C.