we know that to find the number of moles, the following formulae are used:

(i) Using formula 3,

So, 2 moles of copper contain 12.046 x 10²³ atoms of copper.

(ii) Using formula 1,

So, 0.5 moles consist of 27.95 grams of iron.

(iii) Using formula 4,

So, 0.25 moles of CO₂ consists of 1.51 x 10²³ molecules.

Note:

1. If a compound or molecular substance is taken, like CO₂, N₂ etc, then 1

a mole of the substance contains Avogadro number of molecules. 1 mole contains the mass equal to the molecular weight of the substance.

2. If an element is taken like C, S, Fe, then 1 mole contains Avogadro

number of atoms. 1 mole contains the mass equal to the atomic weight of the substance.