Which of the following is an example of an anhydrous product?

An anhydrous product is one that does not contain water. Oil serums are composed primarily of oils and are formulated without the inclusion of water, making them purely anhydrous. This characteristic allows oil serums to provide deep hydration and nourishment to the skin, often preventing moisture loss and supporting the skin's barrier.

In contrast, water-based serums contain water as a primary ingredient, which disqualifies them from being anhydrous. Creams with emulsifiers typically combine both water and oils, meaning they contain water and thus are not anhydrous. Moisturizing gels, while lightweight and often water-based, also contain water, further confirming they do not fit into the anhydrous category. Therefore, oil serums stand out as the only product in the list that is indeed an anhydrous formulation.