CBSE Class 9 Answered

Mole is the unit to measure amount of substance. By number it is equal to 6.02X1023, as this is a huge and uncountable number we convert it to mass which is easily weighed using a balance. If the chemical is in form of atoms 1 mole is equal to atomic mass in grams and if the chemical is molecules than 1 mole is molecular mass in grams. 

 1 mole of carbon is equal to 12g by weight and will have 6.02 x10²³ atoms and in 1 mole of water number of molecules is6.02 x10²³  and weight is 18g.