Q.What is the SI unit of amount of a substance ?

Any quantitative measurement means comparing something against a reproducible, unchanging standard; the arbitrarily-fixed and universally-accepted standard used for this comparison is called a unit. Historically, several parallel unit systems were used side by side — CGS (centimetre, gram, second), FPS (foot, pound, second) and MKS (metre, kilogram, second). In 1960 the General Conference of Weights and Measures adopted a single, unified system, the International System of Units (SI), built on the decimal metric system that originated in eighteenth-century France. SI defines seven independent base physical quantities — len …