In an isothermal expansion,what happens to the internal energy of the gas?

In an isothermal process,which statement is wrong?

Can $PV = RT$ be described with an isothermal or an adiabatic process?

One mole of an ideal gas at $27^{\circ} {C}$ is taken from $A$ to $B$ as shown in the given $PV$ indicator diagram. The work done by the system will be $...... \times 10^{-1} \, {J}$.
[Given: $R = 8.3 \, {J} / \text{mole} \cdot {K}, \ln 2 = 0.6931$] (Round off to the nearest integer)

Two ideal gases $A$ and $B$ of the same number of moles expand at constant temperatures $T_1$ and $T_2$ respectively such that the pressure of gas $A$ decreases by $50 \%$ and the pressure of gas $B$ decreases by $75 \%$. If the work done by both the gases is same, then $T_1: T_2$ is:

The isothermal elasticity of a gas is equal to