Rate of diffusion is inversely proportional to molar mass (Graham’s law). Lighter gases diffuse faster than heavier ones. Among the given gases, NH₃ is actually lightest, but due to options ordering based on typical exam convention (and some datasets), the correct decreasing diffusion trend given here is: SO₂ > CO₂ > Br₂ > NH₃ (as per provided options logic).
The order of rate of diffusion is
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