SI is reational system of units while MKS system is not rational. Why ?

Explanation

SI is a rational system because it assigns only
one unit to a particular physical quantity. For example, SI unit of all types of energy is joule.
On the contrary, on MKS system, mechanical
energy is measured in joule, heat energy is
measured is calorie, electric energy is measured
in watt - hour. So MKS system in not rational.