Question

Which answer does not describe this system at equilibrium?

NO (g) + O2 (g) (arrows pointing opposite ways) 2 NO2 (g)

The rates of the forward and reverse reactions are equal.

The forward reaction does not go to completion.

The reaction is reversible.

The concentration of reactants and products are all equal.

Answer 1

HERE IS YOUR ANSWER

A system in equilibrium indicates that the rate of some forward process within the system is equal to the rate of the corresponding backward process.

This is true whether it is a phase equilibrium, thermal equilibrium, dynamic reaction equilibrium, etc.