What temperature commonly marks the melting point of ice?

• A. 0°C
• B. 100°C
• C. -273°C
• D. 25°C

Answer: (A)

Melting point is the temperature at which a solid becomes a liquid when pressure is kept constant. For ice at standard atmospheric pressure (about 1 atmosphere), that equilibrium occurs at 0 degrees Celsius. Below this temperature, ice remains solid; above it, ice begins to melt into liquid water. This 0-degree mark is the reference melting point for ice under typical conditions.

The other temperatures correspond to different phase changes or conditions: 100 degrees Celsius is the boiling point of water at 1 atm, -273 degrees Celsius is absolute zero (the lowest possible temperature), and 25 degrees Celsius is just ordinary room temperature with no phase change for ice.