A reaction is said to have reached equilibrium when the reaction rate is equal in both directions (c).
Like, take the example of copper in copper sulphate solution. When you add Cu to CuSO4 soln., there won't be any change occurring as the reaction rate is equal (Cu is added to CuSO4 soln., there won't be any change as displacement reaction won't take place due to Cu being the same metal as in CuS04 soln...their reaction is the same).
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