Correct Answer - B
`{:(,XY_(2),hArr,XY,+,Y),("Initial",P,,0,,0),("Final",P-x,,x,,x):}`
Initial `P=600` mm Hg, Final `P=800` mm Hg
Total "moles" `prop` final P.
`:. P-x+x+x prop 800`
`600-x+x+xprop 800`
`x=200` mmHg
`K=(x xx x)/(P-x)=(200xx200)/(400)=100 Hg`