When an object is at infinity from a concave mirror, the image formed is

Options

A. at the focus
B. virtual and erect
C. highly enlarged
D. none of these

Explanation

**Step-by-Step Solution:**

1. **Understanding the Situation**: When an object is placed at infinity from a concave mirror, we need to analyze how the light rays behave when they reach the mirror.

2. **Light Rays from Infinity**: Light rays coming from an object at infinity are considered parallel to the principal axis of the mirror. This is because the distance is so great that the rays can be treated as parallel lines.

3. **Reflection of Light Rays**: According to the laws of reflection, when these parallel rays strike the concave mirror, they reflect and converge towards the focal point of the mirror.

4. **Location of the Image**: Since all the parallel rays converge at the focus after reflection, the image formed when the object is at infinity is located at the focal point of the concave mirror.

5. **Nature of the Image**: The image formed is a real image because the rays of light actually converge at the focal point. A real image is formed when light rays meet at a point.

6. **Size of the Image**: The image size is diminished compared to the object size. Since the object is at infinity, its size can be considered very large, while the image formed at the focus is point-sized.

7. **Conclusion**: Therefore, when an object is at infinity from a concave mirror, the image formed is at the focus, it is a real image, and it is diminished in size.

**Final Answer**: The image formed is at the focus of the concave mirror.

---