(a) Kelvin is the SI unit of temperature. To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature.

Temp. on Kelvin scale = Temp. on Celsius scale + 273

Temp. on Kelvin scale= 25 + 273 = 298 K

Therefore, 25°C = 298 K

(b) Kelvin is the SI unit of temperature. To change a temperature on the Kelvin scale to the Celsius scale you have to subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale you have to add 273 to the given temperature.

Temp. on Kelvin scale= Temp. on Celsius scale + 273 = 373 + 273 = 646 K

Therefore, 373°C = 646 K