At 800 K,K_c for the Following Equilibrium Is 4

Multiple Choice

At 800 K,K_c for the following equilibrium is 4.2 × 10^-3.
2HgO(s)
2Hg(l) + O₂(g)
Suppose 82.3 g of mercury (II) oxide is placed in a sealed 2.50-L vessel at 800 K.What is the partial pressure of oxygen gas at equilibrium? (R = 0.0821 L ∙ atm/(K ∙ mol) )

A) 8.7 atm
B) 4.3 atm
C) 0.27 atm
D) 0.0042 atm
E) 22 atm