Dynamic equilibrium: forward and reverse rates equalize over time

Steps:

• Initially, forward rate is high as X and Y react; reverse rate is zero with no Z present.
• Forward rate decreases as reactants deplete; reverse rate increases as Z accumulates.
• Rates approach each other until they meet and remain constant.
• At equilibrium, forward rate equals reverse rate, maintaining constant concentrations.

Why C is correct:

• Graph shows forward rate decreasing from high initial value, reverse rate increasing from zero, both leveling off at equal constant rates, matching the definition of dynamic equilibrium where net reaction stops.

Why the others are wrong:

• A: Both rates constant from start, ignoring initial absence of Z and rate changes.
• B: Forward rate constant while reverse increases, failing to show reactant depletion.
• D: Rates cross but continue changing, not stabilizing at equilibrium.

Final answer: C