ANS:A - the temperature drops in the two fluids and the wall are proportional to individual resistances.

In a shell and tube heat exchanger, the temperature drop is inversely proportional to the resistance across which the drop occurs. This statement is derived from Fourier's law of heat conduction, which states that the rate of heat transfer (Q) is directly proportional to the temperature difference (ΔT) and inversely proportional to the thermal resistance (R): Q=RΔT​ In a heat exchanger, the temperature drop occurs across various resistances, including those in the fluid streams and the heat transfer surface (wall). According to Fourier's law, the rate of heat transfer (or temperature drop) is inversely proportional to the total thermal resistance encountered by the heat transfer process. Therefore, the correct statement is: "the temperature drop is inversely proportional to the resistance across which the drop occurs."