Water freezes at 0°C. On the Kelvin temperature scale, this is equivalent to

• A. 273 K
• B. 0 K
• C. 373 K
• D. 32 K

Answer: (A)

Kelvin temperatures are just Celsius temperatures plus 273.15, so the freezing point of water converts as 0°C + 273.15 = 273.15 K. In many contexts this is written as 273 K, a rounded value that matches the same point on the Kelvin scale. The other numbers don’t line up with the freezing point: 0 K is absolute zero, far below freezing; 373 K is the boiling point of water at standard pressure (100°C); 32 K is far below typical freezing. So 273 K is the correct equivalent for the freezing point of water.