we know that a dozen is a collection of 12 substances, a century is a collection of 100 substances and a gross is a collection of 144 substances.we use the term dozen,gross etc. to express a certain quantity of a substance. similarly, a mole is a word used to describe a collection of particles i.e. atoms,molecules or ions .
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Mole is the standard unit of amount of any substance. 1 mole of any substance contain 6.022*10 ^23 particles.

eg) 1 mole of Hydrogen atom contain 6.022*10^23 hydrogen atoms.

when 'u' is expressed in grams (g), is the mass of 1 mole of particles.

eg) 16u is the mass of a single atom of oxygen.

16g is the mass of 1 mole of oxygen atoms.

We can calculate the no of moles in 2 ways :

1) Mole = given mass÷ atomic mass or molecular mass
2) Mole = given no of atoms or molecules ÷ 6.022×10^23
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please mark as Brainliest answer .....