Which property of nails may indicate their ability to return to original shape after bending?

The property of nails that indicates their ability to return to their original shape after bending is toughness. Toughness refers to the ability of a material to absorb energy and deform plastically without fracturing. When nails are subjected to bending forces, a tougher material will undergo deformation but can recover its initial shape when the stress is removed.

This quality is essential in nail technology because nails are often subjected to various stresses during their growth and the application of nail products. A tough nail can endure regular use and stress without easily breaking or losing shape.

On the other hand, strength relates to the maximum load a material can withstand before failure, which does not necessarily indicate its ability to return to shape. Hardness is about how resistant a material is to wear and scratching, not its flexibility. Brittleness refers to the tendency of a material to break or shatter under stress rather than deform, making it less able to return to its original shape. Thus, toughness is the correct answer as it encompasses the ability to withstand bending without permanent deformation.