The force $(F)$ required to maintain the flow of layers of a liquid is equal to ($A = \text{area of contact of layers}$, $dz = \text{distance between the layers}$, $du = \text{change in velocity}$, $\eta = \text{coefficient of viscosity}$)

Two balloons $A$ and $B$ containing $0.2 \ mol$ and $0.1 \ mol$ of helium at room temperature and $2.0 \ atm$,respectively,are connected. When equilibrium is established,the final pressure of $He$ in the system is $.... \ atm$.

The rate of diffusion of methane at $1.0 \ atm$ pressure is twice that of another gas '$X$' kept at $1.45 \ atm$. The molecular weight of the gas '$X$' is
[$T$ kept constant]

$A$ $4 : 1$ molar mixture of $He$ and $CH_4$ is kept in a vessel at $20 \ bar$ pressure. Due to a hole in the vessel,the gas mixture leaks out. What is the composition of the mixture effusing out initially?

Fill in the blanks:
$(1)$ Gases like $CO_2$ and $CH_4$ show ............ deviation from ideal gas behavior.
$(2)$ The temperature at which a real gas obeys ideal gas laws over an appreciable range of pressure is called ............ .
$(3)$ The maximum temperature below which a gas can be liquefied is called ............ .
$(4)$ The unit of coefficient of viscosity in the $CGS$ system is ............ .

Densities of two gases are in the ratio $1:2$ and their temperatures are in the ratio $2:1$,then the ratio of their respective pressures is