ANS:B - and the wall are proportional to individual resistances.

In a multipass shell and tube heat exchanger, the temperature drop in the fluid is typically directly proportional to the resistance across which the drop occurs. Each pass in a multipass heat exchanger introduces additional resistance to the flow of the fluid. As the fluid flows through each pass, it experiences a temperature drop due to the resistance encountered along the flow path. Therefore, the temperature drop in the fluid is directly related to the resistance across which the drop occurs. Therefore, the correct statement is: "is directly proportional to the resistance across which the drop occurs."