Identify the reaction described by the following equilibrium expression: K = [H2]2 [O2]/[H₂O]2
a) H₂O (g) <=> H2 (g) + ½ O₂ (g)
b) 2 H₂O (g) <=> 2 H2(g) + O₂ (g)
c) H₂O (g) <=> 2H (g) + O (g)
d) 2 H₂ (g) + O2 (g) <=> 2H₂O (g)