at what time the reaction reached equilibrium?

at what time the reaction reached equilibrium?
Answer
Explanation:
Step1: Recall equilibrium concept
In a chemical - reaction concentration - time graph, equilibrium is reached when the concentrations of reactants and products no longer change with time.
Step2: Analyze the graph
In the given graph, the concentrations of substances a and b stop changing at time $t_3$.
Answer:
$t_3$