Answer: The final concentration of NO be after equilibrium is re‑established is 0.825 M.
Step-by-step explanation:
The given balanced chemical equation is as follows.

Now, equilibrium constant for this reaction will be as follows.
![K_(c) = ([NO]^(2))/([N_(2)][O_(2)])](https://img.qammunity.org/2021/formulas/chemistry/college/fuqm6ujligbwczhf51r74nihan3d0pyusp.png)
It is given that concentrations at the equilibrium are:
= 0.1 M and [NO] = 0.6 M
Therefore, the value of
is as follows.
= 36.0
NO concentration of 0.9 M is added to the system. So,

Initial: 0.1 0.1 0.9
Change: x x 2x
Equibm:(0.1 + x) (0.1 + x) (0.9 - 2x)
Now, we will find the value of x as follows.
36.0 =

x = 0.0375
Therefore, final concentration of NO after the equilibrium that is re-established is as follows.
0.9 - 2x
=

= 0.9 - 0.075
= 0.825 M
Therefore, we can conclude that the final concentration of NO be after equilibrium is re‑established is 0.825 M.