What is the value of the specific heat of a gas during an isothermal process?

The specific heat of a gas in an isothermal process is

The isothermal elasticity of a gas is equal to

During which thermodynamic process does $T$ remain constant, while the other two variables $P$ and $V$ change?

Two identical containers $A$ and $B$ with frictionless pistons contain the same ideal gas at the same temperature and same volume $V$. The mass of the gas in $A$ is $m_{A}$ and that in $B$ is $m_{B}$. The gas in each cylinder is now allowed to expand isothermally to the same final volume $2V$. The changes in the pressures of the gases in $A$ and $B$ are found to be $2\Delta P$ and $3\Delta P$ respectively. Then the relation between $m_{A}$ and $m_{B}$ is

In an isothermal process,the volume of an ideal gas is halved. One can say that: