An ideal gas undergoes adiabatic expansion against constant external pressure. Which of the following is incorrect:

The reversible expansion of an ideal gas under adiabatic and isothermal conditions is shown in the figure. Which of the following statement(s) is (are) correct?

An ideal gas in a thermally insulated vessel at internal pressure $={\mathrm{P}}_1,$ volume $={\mathrm{V}}_1$ and absolute temperature $={\mathrm{T}}_1$ expands irreversibly against zero external pressure, as shown in the diagram. The final internal pressure, volume and absolute temperature of the gas are ${\mathrm{P}}_2, {\mathrm{V}}_2$ and ${\mathrm{T}}_2$, respectively. For this expansion

In an isothermal expansion of a gaseous sample, the correct relation is: (consider $\mathrm{w}$ (work) with sign according to new IUPAC convention)

[The reversible and irreversible processes are carried out between same initial and final states.]