(a) What is meant by 'a mole of carbon atoms' ?
(b) Which has more atoms, 50 g of aluminium or 50 g of iron ? Illustrate your answer with the help of calculations.
(Atomic masses : Al = 27 u ; Fe = 25 u)

(a) A mole can be defined as the amount of a pure substance containing the same number of atoms, molecules or ions as present in exactly 12g of carbon. This refers to the value of 6.022 × 10²³ atoms, molecules or ions of a substance.
Therefore, a mole of carbon atoms refers to a group of 6.022 × 10²³ carbon atoms.

(b)
Mass of aluminium = 50g
We know that 27g of aluminium contain 6.022 × 10²³ aluminium atoms
Number of aluminium atoms in 27g aluminium = 6.022 × 10²³
Number of aluminium atoms in 50g aluminium = 50 × 6.022 × 10²³/ 27
Hence, 50g aluminium has11.15 × 10²³ atoms.

Mass of iron = 50g
We know that 56g iron contain 6.022 × 10²³ atoms
Number of atoms in 56g iron = 6.022 × 10²³
Number of atoms in 50g iron = 50 × 6.022 × 10²³ / 56
Hence, 50g iron comprises 5.376 × 10²³ atoms.
It is clear that more number of atoms is present in 50g aluminium than 50g iron.