For the Endothermic Reaction A₂(g) 2A(g), a Snapshot of an Equilibrium

For the endothermic reaction A₂(g) 2A(g) , a snapshot of an equilibrium mixture of A(g) and A₂(g) may look as follows. (Each circle represents 1.0 mol of A atoms, and the volume of the box is 1.0 L.) What is the equilibrium constant K_c for this reaction at 298 K? (R = 0.08206 L • atm/K • mol)

A) 0.19
B) 0.67
C) 1.3
D) 2.7
E) 5.3