Answer: D. Diffusion rate depends on the mass of the gas particles. Lighter molecules diffuse faster (Graham's law: rate \(\propto 1/\sqrt{M_r}\)).
Statement 2 (molecular formula) is correct because the molecular formula determines the relative molecular mass, and hence the average particle speed. Two gases with the same molecular formula have the same diffusion rate.
Statement 1 (empirical formula) is wrong: empirical formula is just the simplest ratio, so different gases (e.g., ethene \(\text{C}_2\text{H}_4\) and butene \(\text{C}_4\text{H}_8\)) share an empirical formula \(\text{CH}_2\) but have very different molecular masses, and hence different diffusion rates.
Statement 3 (mass of X) is wrong: the total mass of the sample of gas in the corner doesn't affect how fast individual particles spread — only the mass per particle (determined by molecular formula) matters.
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