Presence of a non-condensing gas in a condensing vapour

ANS:D - none of these.

The presence of a non-condensing gas in a condensing vapor does not directly increase the rate of condensation, decrease thermal resistance, or increase the film coefficient. Non-condensing gases in a condensing vapor mixture can actually hinder condensation by diluting the condensable vapor and reducing the partial pressure of the condensable component. This effectively lowers the driving force for condensation and can slow down the condensation process. Additionally, the presence of non-condensing gases can increase the overall thermal resistance of the system by creating a barrier between the condensing vapor and the condensing surface. This increased resistance can impede heat transfer and decrease the efficiency of the condensation process. Therefore, the correct option is: "none of these."