$(1)$ The average kinetic energy of a gas molecule decreases when the temperature is reduced.
$(2)$ The average kinetic energy of a gas molecule increases with increase in pressure at constant temperature.
$(3)$ The average kinetic energy of a gas molecule decreases with increases in volume.
$(4)$ Pressure of a gas increases with increase in temperature at constant pressure.
$(5)$ The volume of gas decreases with increase in temperature.
Choose the correct answer from the options given below:
$Reason :$ When a gas is heated at constant volume some extra heat is needed compared to that at constant pressure for doing work in expansion.
$c_P - c_V = a$ for hydrogen gas
$c_P - c_V = b$ for nitrogen gas
The correct relation between $a$ and $b$ is