AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
It is a concave lens (diverging lens). According to the sign convention, a negative focal length indicates a concave lens.
Source: Chapter 9, Section 9.3.6 Sign Convention for Spherical Lenses
The key rule: focal length of a convex lens is positive and that of a concave lens is negative. Since –12 cm is negative, the lens is concave. Examiners expect you to state the type and give the sign convention reason in one line.