4 g of an ideal gas $A$ (molar mass $=M_A$ ) present in a vessel of volume $V$ litre exerted a pressure of 5 atm at 300 K . When 16 g of another ideal gas $B$(molar mass $=M_B$ ) was introduced into this vessel at the same temperature, its pressure increased to 10 atm . What is the correct relationship between $M_A$ and $M_B$ ?

The ratio of rates of diffusion of gases $X$ and $Y$ of molecular weights 36 and 64 is

Certain volume of oxygen gas diffuses through a porous pot in 20 seconds. Same volume of another gas, $X$ diffuses in $Y$ seconds as that of oxygen, then $X$ and $Y$ respectively are