NEET Chemistry States of Matter / पदार्थ की अवस्थाएँ - गैस एवं द्रव NEET PYQ-States Of Matter

  • question_answer
    50 mL of each gas A and of gas B takes 150 and 200 s respectively for effusing through a pin hole under the similar conditions. If molecular mass of gas B is 36, the molecular mass of gas A will be                                     [AIPMT (S) 2012]

    A)  96                   

    B)       128                 

    C)  32                   

    D)       64

    Correct Answer: D

    Solution :

    Given,               \[{{V}_{A}}={{V}_{B}}=50\,mL\]
    \[{{T}_{A}}=150s\]
    \[{{T}_{B}}=200s\]
    \[{{M}_{B}}=36\]
    \[{{M}_{A}}=?\]
    From Graham's law of effusion
                \[\frac{{{r}_{B}}}{{{r}_{A}}}=\sqrt{\frac{{{M}_{A}}}{{{M}_{B}}}}=\frac{{{V}_{B}}{{T}_{A}}}{{{T}_{B}}\cdot {{V}_{A}}}\]
    \[\Rightarrow \]   \[\sqrt{\frac{{{M}_{A}}}{36}}=\frac{{{V}_{A}}\times 150}{200\times {{V}_{A}}}\]
    or         \[\sqrt{\frac{{{M}_{A}}}{36}}=\frac{15}{20}=\frac{3}{4}\]
                \[\frac{{{M}_{A}}}{36}=\frac{9}{16}\]
    \[{{M}_{A}}=\frac{9\times 36}{16}=\frac{9\times 9}{4}=\frac{81}{4}=20.2\]
     (No option is correct)
    Note If \[{{T}_{A}}=200s\]and\[{{T}_{B}}=150s,\] the \[{{M}_{A}}=64\]


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