The correct answer is : (b) rounded exit.
Among the given options, a rounded exit creates the smallest pressure drop. This is because a rounded exit, often referred to as a smoothly contoured or rounded nozzle, provides a streamlined flow path that minimizes turbulence and disruption to the fluid flow.
As fluid exits through a smoothly contoured nozzle, it experiences less resistance and pressure drop compared to other fittings like elbows (45° or 90°) or tee fittings, which tend to introduce abrupt changes in flow direction, causing greater turbulence and pressure loss.
Therefore, a rounded exit is the most efficient option for minimizing pressure drop in a fluid system.