Ammonium iodide dissociates reversibly to ammonia and hydrogen iodide.

Question

NH4I(s) Picture NH3(g) + HI(g)

At 400°C, Kp = 0.215. Calculate the partial pressure of ammonia at equilibrium when a sufficient quantity of ammonium iodide is heated to 400°C.

Answer 1

What's with the picture stuff? Just put an arrow there.
NH4I(s) ==> NH3(g) + HI(g)
.............p..........p

Kp = pNH3*pHI = 0.215 (what? atm?)
Substitute into Kp and solve for p.