Question

what are S.I units?

Answer 1

systeme international - as called in french. The 'International System of Units'.
This is a standard measure of units. Did you ever think.. 'What is 1kg of mass?' - The scientists came up with a standard amount or a particular number of moles of that substance and said that this is 1kg. Hence, when we say 5kg of something.. we mean 5 lots of that particular amount of that something. This was done to standardize measurement. Or else, people could have taken any amount of something and said this is 1kg.

Answer 2

oh i see..thanks