Question

Which option has the greatest mass?

• A. 0.5 g atom of oxygen
• B. 0.5 mol of O$_3$
• C. 3 $\times$ 10$^{22}$ molecules of nitrogen
• D. 5.6 L of CO$_2$ at STP

Hint:

Convert all quantities to moles, then multiply by the molar mass to find the mass. At STP, 1 mol of any gas occupies 22.4 L.

Answer 1

The Correct Option is B

Option 1: 0.5 g atom of O = 0.5 mol of O atoms = 0.5 × 16 = 8 g.
Option 2: 0.5 mol of O₃ (molar mass of O₃ = 48 g mol^-1) = 0.5 × 48 = 24 g.
Option 3: 3 × 10²² molecules of N₂ = \(\frac{3 \times 10^{22}}{6.022 \times 10^{23}}\) ≈ 0.05 mol, mass = 0.05 × 28 = 1.4 g.
Option 4: 5.6 L of CO₂ at STP (1 mol = 22.4 L) = \(\frac{5.6}{22.4}\) = 0.25 mol, mass = 0.25 × 44 = 11 g.
The highest mass is 24 g, which corresponds to option (2).