What is the meaning of pressure of the gas?

At a constant temperature, gas A (volume V_(A) and pressure P_(A) ) is mixed with gas B (volume V_(B) and pressure P_(B) ). What will the total pressure of the gas mixture be?

A gas is in equilibrium with water at a certain temperature and pressure what will happen if Pressure of the gas is increased ?

What is the effect of pressure on velocity of sound in gas?

What is the value of the pressure coefficient of a gas?