The correct option is B 0.112
The equilibrium number of moles of hydrogen and iodine will be (0.5−x) each respectively.
The equilibrium number of moles of HI will be 2x.
The expression for the equilibrium constant will be 49=(2x0.50−x)2.
Hence, x=0.388.
At equilibrium, the number of moles of iodine unreacted is 0.50−0.388=0.112moles.