Which of the following is an example of a natural food preservative?

Salt is a well-known natural food preservative that has been used for centuries to prolong the shelf life of various foods. It achieves this by drawing moisture out of food and creating an environment that is inhospitable to bacteria and molds, which helps to prevent spoilage. This process is known as osmosis, and it's particularly effective in preserving meats and fish.

While sugar, vinegar, and citric acid also function as preservatives and have their specific roles in food preservation, salt is distinct in its historical and widespread application. Sugar acts primarily as a preservative through its ability to inhibit microbial growth by reducing water activity, vinegar provides acidity that can prevent spoilage, and citric acid serves as an acidulant that can also inhibit bacteria, but salt remains one of the most traditional and commonly recognized methods for preserving food naturally. Thus, salt stands out as a classic example of a natural food preservative.