Multiple effect evaporators ar used to

ANS:B - increase the steam economy & the capacity.

Multiple effect evaporators are used to increase the steam economy and decrease the steam consumption while maintaining or even increasing the overall capacity of the evaporation process. In a multiple-effect evaporator system, the vapor generated in one effect is used to heat the feed in the next effect, thus reducing the need for external heating steam in each successive effect. This cascading effect leads to significant energy savings and improved steam economy compared to single-effect evaporators. Therefore, the correct statement is: "Multiple effect evaporators are used to increase the steam economy and the capacity."