ANS:A - line always lies above the equilibrium curve.

In the case of an absorber, the operating line can be either above or below the equilibrium curve. Explanation:

1. Absorber:
   • An absorber is a unit operation in which a solute from a gas phase is absorbed into a liquid phase.
   • It involves contacting the gas phase containing the solute with a liquid solvent, allowing for the solute to transfer from the gas phase to the liquid phase.
   • The operating conditions of an absorber are determined by factors such as gas and liquid flow rates, temperature, pressure, and the properties of the solute and solvent.
2. Operating Line and Equilibrium Curve:
   • The operating line represents the relationship between the concentrations of the solute in the gas and liquid phases as they change along the height of the absorber.
   • The equilibrium curve represents the equilibrium relationship between the concentrations of the solute in the gas and liquid phases at each stage of the absorber.
   • The position of the operating line relative to the equilibrium curve depends on the specific operating conditions of the absorber.
   • If the operating conditions favor greater solute absorption, the operating line may lie above the equilibrium curve.
   • Conversely, if the operating conditions favor lower solute absorption, the operating line may lie below the equilibrium curve.
3. Velocity Comparison:
   • The comparison of velocities (such as gas velocity and liquid loading velocity) is not directly related to the position of the operating line relative to the equilibrium curve in an absorber.
   • Gas and liquid velocities are important parameters in determining the mass transfer rates and efficiency of the absorber, but they do not dictate the specific position of the operating line.

In summary, the position of the operating line in an absorber can be either above or below the equilibrium curve, depending on the specific operating conditions and the desired level of solute absorption. Therefore, the correct statement is: line can be either above or below the equilibrium curve.