Hi, I just wanted to ask, when writing equilibrium expressions is it necessary to include (aq) or (g) in the expression? And if so, why is the state of the reactants and products different in the equilibrium expression and the reaction in this example? (aq) vs (g). Btw this is the 2017 exam, question 2b (i).
It is definitely good practice to include the physical states in the equilibrium constant expression although omitting them in the exam is not always penalised.
And yes the states in the equilibrium expression definitely must match those in the reaction equation so in your given example I suggest there is a typo in the answers which should all have the (g) physical state.