The correct option is Of the same size as the object.
Explanation
Image formation by a concave mirror is determined by the position of the object relative to the mirror's pole (P), principal focus (F), and centre of curvature (C). The nature, size, and position of the image change as the object moves along the principal axis.
Analysis of the Scenario:
- When an object is placed exactly at the centre of curvature (C) of a concave mirror, the incident rays reflect and converge at the same distance from the mirror.
- The image is formed at the centre of curvature (C).
- The characteristics of the image in this specific position are:
- Nature: Real and Inverted.
- Size: Same size as the object.
Comparison with Other Positions:
- Highly diminished/Point-sized: This occurs when the object is placed at infinity.
- Enlarged: This occurs when the object is placed between the centre of curvature (C) and the principal focus (F).
Key Takeaway:
For a concave mirror, the centre of curvature (C) is the unique object position where the resulting image is real, inverted, and of the same size as the object.