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Top Answer by best Chemistry Teacher in patna , IITian Rishi Sir

Definition of 1 mole by best chemistry teacher in patna, IITian Rishi Sir 

A mole is the amount of a substance that contains as many entities (atoms, molecules or other particles) as there are atoms in exactly 0.012 kg (or 12 g) of the carbon-12 isotope.

            From mass spectrometer we found that there are 6.023 × 1023 atoms present in 12 g of C-12 isotope.

            The number of entities in 1 mol is so important that it is given a separate name and symbol known as Avogadro constant denoted by NA.

            i.e. on the whole we can say that 1 mole is the collection of 6.02 × 1023 entities. Here entities may represent atoms, ions, molecules or even pens, chair, paper etc also include in this but as this number (NA) is very large therefore it is used only for very small things.