When detergent is added to pure water, the surface tension decreases; option [B]. Detergent molecules contain both hydrophilic and hydrophobic components. The hydrophilic part interacts with water molecules, while the hydrophobic part disrupts the cohesive forces between water molecules at the surface. As a result, the surface tension of the water decreases, allowing the detergent solution to spread more easily over surfaces and penetrate materials for effective cleaning. This reduction in surface tension enhances the detergent’s ability to wet surfaces and lift away dirt and grease. Consequently, adding detergent to water improves its cleaning properties compared to pure water alone. This phenomenon is widely utilized in various applications, from household cleaning to industrial processes, where reducing surface tension is essential for achieving thorough and efficient cleaning results.