HCI 07 prelims P1 Q4

This is a brilliant question. Now the key is, water and Iodine will condense (to liquid and solid respectively) when the temperature is cooled to room temp (298K). So all the gas thats remaining is Argon. Therefore the no of mols of gas, n, is totally accounted by argon.
using the eqn, nR=p1V1/T1=p2V2/T2, where p1 is 101kPa, V1 is 4000 cm3(thats the volume occupied initailly by argon), T1 is 423K (thats 150 C), p2 is new pressure, V2 is 14090 cm3(the argon expands into all 3 containers) and T2 is 298K
we get p2 = 101(4000)(298)/(423)(14090), => p2 is 20.2 kPa. essentially, this p2 is the new pressure of argon after it has been allowed to expand to all 3 containers, followed by cooling to room temp. We do not consider the other cpds because they no longer exist as gas at the end of the day anyway.