AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
(C) Concave, with radius of curvature 24 cm
A negative focal length indicates a concave mirror. Using $R = 2f$: $R = 2 \times 12 = 24$ cm.
In the New Cartesian Sign Convention, a negative focal length means the focus lies in front of the mirror — this is a concave mirror. The formula $R = 2f$ (magnitude only for R) gives $R = 24$ cm. Students often confuse sign of focal length with mirror type: remember, concave → negative $f$; convex → positive $f$.