Oxygen molecules are 16 times more massive than hydrogen molecules. At a given temperature, how do their average molecular speeds compare? The oxygen molecules are moving

The zeroth law of thermodynamics:  If two systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.

Boyle's law: The volume of a gas is inversely proportional to the absolute pressure applied to it when the temperature is kept constant.
Charles's law: The volume of a given amount of gas is directly proportional to the absolute temperature when the pressure is kept constant.
Gay-Lassac's law: At constant volume, the absolute pressure of a gas is directly proportional to the absolute temperature.