If Q < K, the system is not at equilibrium and Reactants Products.
The ratio of product concentrations
to reactant concentrations is too small.
More reactants must be converted to products (thus increasing Q) to achieve equilibrium (when Q = K).
If Q = K, the system is at equilibrium.
If Q > K, the system is not at equilibrium and Products Reactants.
The ratio of product concentrations
to reactant concentrations is too large.
To reach equilibrium, products must be converted to reactants (thus decreasing the value of Q until Q = K).
The value of Qc is less than the value of Kc (Qc < Kc), so the reaction is not at equilibrium. It must proceed to equilibrium by converting more NO2 to N2O4, thus increasing [N2O4] and decreasing [NO2] until Qc = Kc.