An amount of solid NH4HS is placed in a flask already containing ammonia gas at a
certain temperature and 0.50 atm. Pressure. Ammonium hydrogen sulphide
decomposes to yield NH₃ and H₂S gases in the flask. When the decomposition
reaction reaches equilibrium, the total pressure in the flask rises to 0.84 atm. The
equilibrium constant for NH₄HS decomposition at this temperature is :