Which of the following,in general,is a slow process?

Can two isothermal curves intersect each other?

The temperature of an ideal gas is kept constant as it expands. The gas does external work. During this process,the internal energy of the gas

If an ideal gas is compressed isothermally,then:

For an isothermal expansion of a perfect gas,the value of $\frac{\Delta P}{P}$ is equal to:

The internal energy of an ideal gas increases during an isothermal process when the gas is