What is the SI unit of mass? How is it defined?
The SI system was internationally accepted in 1960. SI is the abbreviation of “System International” Units which is French equivalent of “International System of Units”.
The SI unit of Mass is kilogram.
1 kilogram is defined as the mass of a platinum-iridium cylinder kept in Paris.
In practice, the mass of 1litre of water at 4°C is 1 kilogram.
On atomic scale, 1 kilogram is equivalent to the mass of 5.0188× 1025 atoms of 6C12 [isotope of carbon].