Answer:
Constant number of particles and concentration, equal forward and reverse reaction rates
Explanation:
In order to properly answer this question, we need to define the state of equilibrium in terms of its characteristics:
Given this equilibrium system, when equilibrium is reached, the moles, the number of particles and the molarity of methane, hydrogen sulfide, carbon disulfide and hydrogen gas, they all become constant and don't change over time. When equilibrium is established, molarity values don't change, and since molarity is directly proportional to the number of moles (as well as the number of atoms), the latter don't change too.
In terms of the reaction rate, it is true for any equilibrium system, including the one defined, that the forward reaction rate (reaction between methane and hydrogen sulfide) becomes equal to the reverse reaction rate (reaction between carbon disulfide and hydrogen gas).