Answer: 
 at the temperature of the experiment is 0.56.
Step-by-step explanation:
Moles of 
 = 0.35 mole 
Moles of 
 = 0.40 mole 
Volume of solution = 1.00 L 
Initial concentration of 
 = 
 
Initial concentration of 
 = 

Equilibrium concentration of 
 = 
 
The given balanced equilibrium reaction is, 
 
 
Initial conc. 0.35 M 0.40 M 0 M 0M 
 At eqm. conc. (0.35-x) M (0.40-x) M (x) M (x) M
Given: (0.35-x) = 0.19
x= 0.16 M
 The expression for equilibrium constant for this reaction will be, 
 
Now put all the given values in this expression, we get : 
 

Thus 
 at the temperature of the experiment is 0.56.