ANS:C - account for the uneven expansion of shell and tube bundles.

The purpose of providing expansion bellows in the shell of a tubular exchanger is to account for the uneven expansion of the shell and tube bundles. During operation, the temperature of the fluid inside the tubes and the shell may vary, causing differential expansion between the shell and the tube bundle. This differential expansion can lead to stress concentrations and potential damage to the equipment if not properly accommodated. Expansion bellows are flexible components that allow for the controlled expansion and contraction of the shell, thereby mitigating the effects of thermal expansion and ensuring the structural integrity of the exchanger. Therefore, the correct option is: account for the uneven expansion of shell and tube bundles.