The focal length ($f$) is the distance from the mirror's pole to the principal focus.

The center of curvature ($C$) is the center of the sphere of which the mirror is a part.

This relationship ($R = 2f$) is valid for both concave and convex mirrors.

The SI unit for both focal length and radius of curvature is the meter (m), though centimeter (cm) is common in optics problems.

This relation allows for easy calculation of optical parameters in ray tracing.

This formula is only an approximation valid for paraxial rays (rays close to the principal axis).

Designing telescope mirrors.

Calculating magnification and image position in headlights and shaving mirrors.

If $f = 12 \text{ cm}$, then $R = 2 \times 12 = 24 \text{ cm}$.

Option A ($3 \text{ cm}$) is incorrect as it assumes $f/4$.

Option C ($2 \text{ cm}$) is incorrect as it assumes $f/6$.

Option D ($6 \text{ cm}$) is incorrect as it assumes $f/2$.