CBSE Class 9 Answered

1 mole of a substance is equal to its atomic mass or molecular mass expressed in grams.

•  The molecular mass of oxygen (O₂) =  2 × Atomic mass of oxygen

                                                                                              = 2 × 16 = 32 g

               So, 32 grams of oxygen is equal to one mole of oxygen molecule.

1 mole of a substance is equal to 6.022  X 10²³ particles i.e. atoms, molecules or ions of the substance.

A mole is defined as the amount of a substance containing elementary particles like atoms, molecules or ions in 12 gram of carbon-12 (¹²C).