On average, how much does a thumb nail grow in a year?

The average growth rate for fingernails, including thumb nails, is about 0.1 inches per month. Over the course of a year, this translates to approximately 1.2 inches of growth. Therefore, the choice indicating that a thumb nail grows around 1.5 inches in a year is the most accurate representation of this average growth rate. This growth can vary based on factors such as age, health, and nutrition, but 1.5 inches serves as a reasonable estimate for the average growth of a thumb nail over a 12-month period.