Ammonium Iodide Dissociates Reversibly to Ammonia and Hydrogen Iodide

Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide. NH₄I(s) ⇄ NH₃(g) + HI(g)
At 400°C, K_p = 0.215. Calculate the partial pressure of ammonia at equilibrium when a sufficient quantity of ammonium iodide is heated to 400°C.

A) 0.103 atm
B) 0.215 atm
C) 0.232 atm
D) 0.464 atm
E) 2.00 atm