21. The reactionN2(g) + 3H2(g) 2NH3(g)takes place in a 1.0-L vessel initially filled with an equimolar mixture of N2 and H2 at a pressure of 12.0 atm. When equilibrium is reached, the partial pressure of H2 is 3.0 atm. Determine the value of Kp for this reaction.
(A)0.915
(B)0.333
(C)0.133
(D)0.030