1.0 mol of $\mathrm{PCl}{}_5(\mathrm{g})$ dissociates ($\mathrm{PCl}{}_5(\mathrm{g})\rightleftharpoons \mathrm{PCl}{}_3(\mathrm{g})+\mathrm{Cl}{}_2(\mathrm{g})$) to the extent of 50% at a total equilibrium pressure of 1.00 atm and temperature $T$. Which statements are correct?

1. A$K_p=0.333$ atm at $T$
2. BThe mole fraction of $\mathrm{PCl}{}_5$ at equilibrium is 0.50
3. CAt the same $T$ and a total pressure of 4.00 atm, the degree of dissociation is about 0.28
4. DAt the same $T$ and a total pressure of 4.00 atm, the degree of dissociation is exactly 0.25