ICSE Class 9 Answered

Kelvin is the fundamental unit of the Kelvin scale. At an absolute temperature scale has its zero point absolute zero value. The values on such scale are non-negative due the theoretical temperature at which the molecules of a substance have the lowest energy.

The 'standard temperature' we use is the temperature of the triple point of water, which is the exclusive temperature at which the three phases of water  i.e. solid, liquid and vapour  co-exist in equilibrium. We define this temperature to be 273.16. Hence, kelvin(K)  taken   as   fundamental   unit   of   Temperature.