Equilibrium constant

Which of the following pairs of chemical equation and equilibrium constant expression is/are CORRECT?

1. 4 Bi (s) + 3 O2 (g) 2 Bi2O3 (s), K = [O2]3

2. Ba (s) + 2 H+ (aq) Ba2+ (aq) + H2 (g), K = [Ba2+][H2] / [H+]

3. Ti (s) + 2 Cl2 (g) TiCl4 (l), K = 1/[Cl]2

4. 4 NH3 (g) + 5 O2 (g) 4 NO (g) + 6 H2O (l), K = PNO4 / PNH34 PO25
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