Q21 / 160 · AP EAMCET 2005 · Chemistry

$A$ and $B$ are ideal gases. The molecular weights of $A$ and $B$ are in the ratio of $1: 4$. The pressure of a gas mixture containing equal weights of $A$ and $B$ is $P$ atm. What is the partial pressure (in atm) of $B$ in the mixture?

  • Correct answer
    A
    $\frac{P}{5}$
  • B
    $\frac{P}{2}$
  • C
    $\frac{P}{2.5}$
  • D
    $\frac{3 P}{4}$

Solution

Mol. wt. ratio of $A$ and $B=1: 4$ $\therefore$ mole ratio of $A$ and $B$, if equal weight of $A$ and $B$ are taken $=4: 1$ $\begin{aligned} \therefore \text { partial pressure of } B & =\frac{1}{(1+4)} \times P \\ & =\frac{P}{5} \end{aligned}$

Hence, the correct answer is option: 'A'.

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