Answer : The correct option is, (E) 7.8 atm
Explanation :
The partial pressure of  = 8.00 atm
 = 8.00 atm
The partial pressure of  = 5.00 atm
 = 5.00 atm
 = 0.0025
 = 0.0025
The balanced equilibrium reaction is,
                                
Initial pressure     8.00      5.00            0
At eqm.               (8.00-x) (5.00-x)        2x
The expression of equilibrium constant  for the reaction will be:
 for the reaction will be:

Now put all the values in this expression, we get :

By solving the terms, we get:

The equilibrium partial pressure of  = (8.00 - x) = (8.00 - 0.15) = 7.8 atm
 = (8.00 - x) = (8.00 - 0.15) = 7.8 atm
Therefore, the equilibrium partial pressure of  is 7.8 atm.
 is 7.8 atm.