What is the relationship between viscosity and density?

At constant temperature,$200 \ cm^3$ of $N_2$ at $720 \ mm$ pressure and $400 \ cm^3$ of $O_2$ at $750 \ mm$ pressure are taken in a $1 \ L$ flask. What will be the total pressure of the mixture in $mm$?

Assertion : Wet air is heavier than dry air.
Reason : The density of dry air is more than density of water.

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 ............ .

Which of the following gas mixtures is not applicable for Dalton's law of partial pressure?

The combination of plots which do not represent isothermal expansion of an ideal gas is