At constant volume and temperature conditions,the rate of diffusion $D_A$ and $D_B$ of gases $A$ and $B$ having densities $\rho_A$ and $\rho_B$ are related by the expression:

Fill in the blanks:
$(1)$ The properties of gases were first measured by ......... .
$(2)$ The dipole-dipole interaction energy between stationary polar molecules is proportional to .......... .
$(3)$ The interaction energy between rotating polar molecules is proportional to .......... .
$(4)$ The bond energy of a hydrogen bond is about ......... $kJ \ mol^{-1}$.

What is the density of water vapour at the boiling point of water?

On the top of a mountain,water boils at

If $X \, mL$ of $H_2$ gas diffuses through a hole in a container in $5 \, s$,what is the time taken for the diffusion of the same volume of another gas under identical conditions?

When the temperature is raised,the viscosity of a liquid decreases. This is because: