Answer: B. Under the same conditions, two gases diffuse at the same rate only when they have the same relative molecular mass (lighter molecules diffuse faster, since rate \(\propto 1/\sqrt{M_r}\)).
\(M_r(\text{N}_2) = 2 \times 14 = 28\). Checking the options: \(M_r(\text{CO}) = 12 + 16 = 28\) (matches), \(M_r(\text{CO}_2) = 44\), \(M_r(\text{Ne}) = 20\), \(M_r(\text{SO}_2) = 64\).
Only carbon monoxide has the same \(M_r\) as nitrogen, so it diffuses at the same rate. Answer B.
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