In which of the processes does the internal energy of the system remain constant?

When heat is given to a gas in an isothermal change,the result will be

An isothermal process has a non-linear graph between:

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

When heat is given to a gas in an isothermal process,then there will be

During an isothermal expansion of an ideal gas,