Explanation:

5 cm, converging.

• The focal length of a lens is the distance between the lens and its focal point.
• In this case, since the image is formed at the same size as the object, we can conclude that the image distance is the same as the object distance, which is 10 cm.
• Using the lens formula 1/f = 1/v - 1/u, where f is the focal length, v is the image distance, and u is the object distance, we can substitute the given values to find the focal length.
• Using the formula, 1/f = 1/10 - 1/(-10) = 1/10 + 1/10 = 2/10 = 1/5.
• Therefore, the focal length is 5 cm.
• Based on the focal length, we can determine the nature of the lens. A converging lens has a positive focal length, while a diverging lens has a negative focal length. In this case, since the focal length is positive (5 cm), the lens is converging.