(i) 1 mole of Ar contains 6.022 × $10^{23}$ atoms 52 moles of Ar contains 52 × 6.022 × $10^{23}$ = 3.13 × $10^{25}$ atoms (ii) 4 u of He = 1 atom 52 u of He = $\frac{1}{4}$ × 52 = 13 atoms (iii) 4 g of He contains 6.022 × $10^{23}$ atoms 52 g of He contains $\frac{6.022\times10^{23}}{4}$ × 52 = 7.83 × $10^{24}$ atoms