NEET 2020 Chemistry Question 123 Solution

For any substance of mass $$m$$: $$\text{Number of moles of molecules/atoms } n = \frac{m}{M}$$ $$\text{Total number of atoms} = n \times \text{Atomicity} \times N_A = \left(\frac{m}{M}\right) \times \text{Atomicity} \times N_A$$

1. For $$1\text{ g of Ag (s)}$$ ($$\text{Atomic mass} = 108\text{ g mol}^{-1}$$, atomicity = 1): $$\text{Atoms} = \frac{1}{108} N_A \approx 0.00926 N_A$$ 2. For $$1\text{ g of Mg (s)}$$ ($$\text{Atomic mass} = 24\text{ g mol}^{-1}$$, atomicity = 1): $$\text{Atoms} = \frac{1}{24} N_A \approx 0.04167 N_A$$ 3. For $$1\text{ g of } \text{O}_2\text{ (g)}$$ ($$\text{Molar mass} = 32\text{ g mol}^{-1}$$, atomicity = 2): $$\text{Atoms} = \left(\frac{1}{32}\right) \times 2 \times N_A = \frac{1}{16} N_A \approx 0.06250 N_A$$ 4. For $$1\text{ g of Li (s)}$$ ($$\text{Atomic mass} = 7\text{ g mol}^{-1}$$, atomicity = 1): $$\text{Atoms} = \frac{1}{7} N_A \approx 0.14286 N_A$$

$$0.14286 N_A > 0.06250 N_A > 0.04167 N_A > 0.00926 N_A$$ Clearly, 1 g of lithium possesses more than double the number of atoms compared to 1 g of oxygen gas, and over 15 times that of silver.

Option (4) contains the maximum number of atoms.