To decide the outcome of this reaction, we need to know the state of the products, as in if they are solid, liquid, gaseous, aqueous, etc. The proper reaction is as follows:
If we were to look up the species CoSO₄ and NaCl, we would find that both of these species are also aqueous. Therefore, neither CoSO₄ or NaCl will precipitate from the solution, so we can ignore options A and B. Neither species formed is gaseous either, therefore, it cannot be option C. That leaves us with option D as the answer.
D is the correct answer because the product of the double displacement is the formation of two more aqueous species which will remain dissociated in the aqueous solution leading to no chemical reaction overall.
