When iron was dissolved in hot concentrated sulfuric acid, 16.8 L of sulfur dioxide was released. The mass of the reacted iron is

the number of moles of sulfur dioxide = 16.8 / 22.4 = 0.75 mol
the number of moles of iron = 0.75 * 2/3 = 0.5 mol
iron mass = 0.5 * 56 = 28 g

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