CBSE Class 9 Answered

A mole is the quantity of an element that you have when you weigh out in grams the amount of that element specified by the atomic weight. The special property of a mole is that one mole of an element contains the same number of atoms as one mole of any other element, even though at this moment we don't know what number of atoms that happens to be.

The mole is the amount of a substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12; its symbol is "mol." When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.