The rate of diffusion of a gas Y is twice that of Z. If the relative molecular mass of Y is 64 and the two gases diffuse under the same conditions, find the relative molecular mass of Z.
32
4
8
16
0
Correct answer: 16
Explanation: By Graham’s law, diffusion rate is inversely proportional to the square root of molar mass: \( r \propto \frac{1}{\sqrt{M}} \). If gas Z diffuses twice as fast as gas Y, then \( \frac{r_Y}{r_Z}=\frac{1}{2}=\sqrt{\frac{M_Z}{M_Y}} \). Squaring: \( \frac{1}{4}=\frac{M_Z}{64} \Rightarrow M_Z=16 \).
Note: If one reads the statement as “Y diffuses twice as fast as Z” (i.e., \( r_Y=2r_Z \)), then \( M_Z=256 \), which is not among the options; JAMB versions of this item usually intend the faster gas to be Z.
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