Why are liquids and gases categorised as fluids?

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

$A$ container consists of a mixture of four gases: $5 \text{ g } H_2$,$8 \text{ g } He$,$50 \text{ g } CO_2$,and $20 \text{ g } Ne$ at a certain temperature. Which of the following gases exerts the minimum partial pressure?

$A$ closed vessel contains an equal number of nitrogen and oxygen molecules at a pressure of $P \ mm$. If nitrogen is removed from the system,then the pressure will be

What is saturated vapor pressure?

$A$ neon-dioxygen mixture contains $64 \ g$ $O_2$ and $160 \ g$ $Ne$. If the total pressure is $25 \ bar$,calculate the partial pressure of dioxygen. (in $bar$)