Answer:
Kp is 2.98 (option c.)
Explanation:
The decomposition is:
NH₄NO₃(s) → N₂O(g) + 2H₂O(g)
Total pressure at equilibrium is 2.72 bar so, in order to determine Kp we need the partial pressure and we only have total pressure.
According to stoichiometry, nitrogen oxide increase by 1, the partial pressure and water vapor, by 2.
Total pressure is: Partial pressure N₂O + Partial pressure H₂O
2.72 bar = X + 2X → X = 2.72 bar / 3 = 0.91 bar
Partial pressure N₂O = 0.91 bar
Partial pressure H₂O = 1.81 bar
We make the expression for Kp = Partial pressure N₂O . (P. pressure H₂O)²
Kp = 0.91 . 1.81² = 2.98
We do not consider the ammonium nitrate, because it is solid