Which of the following is a sign of a healthy nail?

A sign of a healthy nail is characterized by its firm structure, shiny appearance, and a slightly pink color. Each of these attributes indicates that the nail is well-nourished and has a healthy blood supply underneath, contributing to its overall appearance. The firmness suggests that the nail is not brittle or weak, while the shine indicates proper moisture and lack of damage. The pink hue is representative of a good circulation of blood in the nail bed, further confirming its health.

In contrast, notched surfaces with deep grooves suggest damage or possible underlying health issues, while flexibility without strength can be a sign of unhealthy nails. Similarly, deep ridges indicate irregular growth or nutritional deficiencies. Therefore, the qualities described in that choice distinctly align with the characteristics of a healthy nail.