Determine the rate of consumption of A in the forward reaction.

Since the reaction is elementary, the stoichiometric coefficients are the reaction orders. The rate of reaction for a species $A$, denoted as $r_A$, is the net rate of change of its concentration.

Step 1: Determine the rate of consumption of A in the forward reaction.
The forward reaction is $2A + B \xrightarrow{K_f} C + 2D$.
For an elementary reaction, the rate law is determined by the stoichiometric coefficients of the reactants.
The rate of the forward reaction is $r_f = K_f C_A^2 C_B^1$.
Since A is a reactant, it is consumed. The rate