What is an ideal gas in the context of kinetic molecular theory?

According to the first postulate of kinetic molecular theory, how does the volume of gas particles compare to the volume of the container?

If the temperature of a gas is increased, what happens to the velocity of its molecules according to the second postulate of kinetic molecular theory?

What is meant by elastic collisions in the context of the third postulate of kinetic molecular theory?

Calculate the root mean square speed of oxygen molecules at 300 K. (Molar mass of O₂ = 32 g/mol, R = 8.314 J/mol·K)