# 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 ?

$\begin {array} {1 1} (a)\;\frac{P}{5} & \quad (b)\;\frac{P}{2} \\ (c)\;\frac{P}{2.5} & \quad (d)\;\frac{3P}{4} \end {array}$