What is typically applied to ensure that nail polish adheres well?

The correct answer is the base coat, which plays a crucial role in the nail polish application process. A base coat is specifically formulated to create a smooth surface on the nails, allowing the nail polish to adhere better and last longer. It helps to prevent staining of the natural nail from colored polishes and promotes a more even application of the color on top. Moreover, base coats often contain ingredients that can strengthen the nails and enhance the overall appearance of the manicure.

In contrast, a top coat is designed to be applied after the nail polish to provide a protective layer, enhance shine, and prolong the wear of the manicure. Nail hardeners are used to strengthen weak or brittle nails, while cuticle oil is intended to moisturize and nourish the cuticles, but none of these products serve the primary function of promoting adherence of nail polish, which is the main purpose of a base coat. This distinction highlights the importance of each product in the manicure process.