Which is the only condition under which a concave mirror forms a virtual and upright image on the principal axis?
a when an object is placed at the focal point on the principal axis
b. when an object is placed at the center of curvature on the principal axis
c. when an object is placed between the center of curvature and focal point on the principal axis
d. when an object is placed between the focal point and the vertex of the mirror

The only condition under which a concave mirror forms a virtual and upright image is when an object is placed between the center of curvature and the focal point on the principal axis.

Explanation:

Concave or converging mirrors are recessed inward and hence reflect light to an inward focal point. Depending on the distance of the objects from the focal point and the center of curvature of the concave mirror; the image reflects at various positions.

On placing the object between the focal point and the center of curvature of the concave mirror, we get a virtual upright image away from the focal point on the principal axis behind the mirror. In this position we get a larger image.

We can find this image on a ray diagram by tracing the reflected rays backward where they all meet.

answer///terminator or twilight zone;