Which temperature is defined as Absolute Zero?

• A. 0°C
• B. 0 K
• C. Positive 273°C
• D. Negative 273 K

Answer: (B)

Absolute zero is the lowest possible temperature, where molecular motion becomes minimal. On the Kelvin scale this is 0 kelvin. Because Kelvin and Celsius are linked by K = C + 273.15, 0 kelvin equals about -273.15°C. So 0°C is not absolute zero; it is 273.15 degrees warmer than it. The other options aren’t correct: a temperature of 273°C is very hot, and negative 273 kelvin isn’t a valid temperature on the Kelvin scale. In practice, scientists can approach absolute zero very closely but cannot reach it exactly.