ANS:C - can lie above or below the equilibrium curve.

For stripping of a gas in a counter-current stripper, the operating line typically lies above the equilibrium curve. Here's why:

• In a counter-current stripper, the gas stream is contacted with a liquid solvent in order to remove a particular component from the gas stream.
• The equilibrium curve represents the relationship between the composition of the gas phase and the composition of the liquid phase at equilibrium.
• The operating line represents the actual relationship between the compositions of the gas and liquid phases at each stage of the stripper.
• During stripping, the gas phase is typically richer in the component to be removed compared to the liquid phase. As a result, the operating line lies above the equilibrium curve.
• This positioning of the operating line ensures that the gas phase leaving each stage of the stripper is in equilibrium with the liquid phase at that stage, allowing for efficient mass transfer.