• # question_answer 50 mL of each gas A and of gas B takes 150 and 200 seconds respectively for effusing through a pin hole under the similar condition. It molecular mass of gas B is 36, then the molecular mass of gas A will be A)  96           B)  128C)  32           D)  64

${\frac{{{V}_{A}}}{{{t}_{A}}}}/{\frac{{{V}_{B}}}{{{t}_{B}}}}\;=\sqrt{\frac{{{M}_{B}}}{{{M}_{A}}}}$ $\Rightarrow$$\frac{200}{150}=\sqrt{\frac{36}{{{M}_{A}}}}\Rightarrow \frac{4}{3}=\sqrt{\frac{36}{{{M}_{A}}}}$ $\Rightarrow$$\frac{16}{9}=\frac{36}{{{M}_{A}}}\Rightarrow \frac{81}{4}=20.25$ So, most approximate answer is 32.