What temperature is defined as absolute zero?

Absolute zero is defined as the point at which the motion of atoms theoretically comes to a complete stop, representing the lowest possible temperature. In the Kelvin scale, absolute zero is defined as 0 K, which corresponds to -273.15°C. Therefore, -273°C is commonly approximated to -273°C when we consider absolute zero in many contexts, making it the correct option.

At absolute zero, a substance possesses minimum thermal energy. This temperature is a critical reference point in thermodynamics and is significant for understanding the behavior of gases, as gas laws portray the relationship between pressure, volume, and temperature. The other options do not represent absolute zero accurately. For instance, 0°C is the freezing point of water, 273 K is equivalent to 0°C, and -459°F is a much colder temperature, but it does not give the equivalent temperature in the Celsius scale directly associated with the absolute zero concept.