ANS:D - Both (b) and (c)

In the McCabe-Thiele method, one theoretical stage is typically considered equivalent to either a total condenser or a reboiler. A total condenser is a condenser that condenses all the vapor coming out of the top of the column into a liquid, returning it as reflux to the top of the column. This effectively represents one theoretical stage in the distillation process. A reboiler, on the other hand, is a heat exchanger at the bottom of the distillation column that provides heat to vaporize the liquid mixture in the column's bottom tray. It allows the vaporized liquid to rise up through the column, separating into its components as it ascends. A reboiler also represents one theoretical stage in the distillation process. So, both option (b) and (c), total condenser and reboiler, are considered equivalent to one theoretical stage in the McCabe-Thiele method.