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# The relative rates of diffusion of gas B as compared to that of diatomic gas A is 6.5. Find the molecular weight of B if atomic weight of A is 36.

$(a)\;2.3\qquad(b)\;2.6\qquad(c)\;1.7\qquad(d)\;2.9$

Atomic weight of A = 36
Molecular weight of A = $36\times2 = 72$
From Graham's law , rate of diffusion 'r'
$\large\frac{r_A}{r_B} = \sqrt{(\large\frac{M_B}{M_A})}$
$\therefore r_B = 6.5r_A$
$\therefore \large\frac{1}{6.5} = \sqrt{\large\frac{M_B}{72}}$
$\therefore M_B = 1.7$