Why can synthetic detergents be used instead of natural soaps?

The correct choice highlights that both synthetic detergents and natural soaps lower the surface tension of water, which is one of the critical functions these substances perform. Lowering the surface tension helps in the effective cleaning of surfaces by allowing water to spread and penetrate more easily into the dirt or oils, lifting them away.

While it's true that natural soaps also serve this function, synthetic detergents generally contain surfactants that can be engineered to enhance cleaning effectiveness beyond what traditional soaps can achieve. This engineered approach means that synthetic detergents can be effective in a variety of conditions, including hard water, where natural soaps may struggle to work effectively.

The other options can lead to misunderstandings about the comparative benefits. Although synthetic detergents may often be cheaper and have varying environmental impacts depending on the formulation, these characteristics do not specifically address their cleaning functions. Additionally, it's essential to note that while some synthetic detergents are biodegradable, this is not universally true, and not all natural soaps are biodegradable either. Focusing on their functional similarity of reducing water surface tension is crucial in understanding why synthetic detergents might be preferred in specific contexts.