ANS:B - lowest in last effect

In a forward feed multiple-effect evaporator, the pressure typically decreases from the first effect to the last effect. Here's why:

1. Forward Feed: In a forward feed multiple-effect evaporator, the feed enters the first effect, and the concentrated solution from the first effect becomes the feed for the second effect, and so on. Therefore, the solution flows in the forward direction from the first effect to the last effect.
2. Pressure Decrease: As the solution progresses through each effect, water evaporates, leading to an increase in concentration and a decrease in temperature. Because vapor pressure is a function of temperature, the decreasing temperature results in decreasing vapor pressure. Consequently, the pressure in each successive effect is lower than the previous one.
3. Highest Pressure in First Effect: The highest pressure is typically in the first effect, where the feed enters the evaporator. This is because the pressure in subsequent effects is reduced due to the decrease in temperature caused by the evaporation process.