Two moles of a diatomic ideal gas ($C_V=\frac{5}{2}R$) at $400\mathrm{K}$ and $5\mathrm{bar}$ expand adiabatically to $1\mathrm{bar}$, once irreversibly against a constant external pressure of $1\mathrm{bar}$ and once reversibly. Which statement is correct?

1. A$T_{irrev}\approx 253\mathrm{K}$, $T_{rev}\approx 309\mathrm{K}$, and the gas does more work in the reversible expansion
2. B$T_{irrev}\approx 309\mathrm{K}$, $T_{rev}\approx 253\mathrm{K}$, and the gas does more work in the irreversible expansion
3. C$T_{irrev}\approx 309\mathrm{K}$, $T_{rev}\approx 253\mathrm{K}$, and the gas does more work in the reversible expansion
4. D$T_{irrev}=T_{rev}\approx 253\mathrm{K}$, and the work done is the same