Calculate the number of atoms in each of the following:

(i) 52 moles of Ar

(ii) 52 u of He

(iii) 52 g of He.

(i) According to Avogadro’s Law,

1 mole of Argon → 6.023×10²³ atoms of Argon

So, 52 moles of Argon → X atoms of Argon

X =52×6.023×10²³

=3.13196×10²⁵

Therefore in 52 moles of Argon 3.13196×10²⁵ atoms are present.

(ii) Atomic Mass of Helium [He] = 4 u

This means that mass of one atom of Helium is = 4 u

So, Number of atom of Helium contained in 52u = 52/4

= 13 atoms

Therefore, in 52u of Helium 13 atoms are present.

(iii) Atomic Mass of Helium [He] = 4 u

So, Number of Moles of Helium in 52g = 52/4

= 13 atoms

So, Number of atoms in 52g of Helium [He] = 13×6.023×10²³

= 7.8299×10²⁴

Therefore, in 52g of Helium 7.83×10²⁴ atoms are present.