When an object is placed at infinity in front of a convex mirror, what is the nature of the image formed?

The correct answer is Virtual and erect.

Step 1: Understand the position of the object
When an object is placed at infinity in front of a convex mirror, the incident light rays coming from the object are parallel to the principal axis.

Step 2: Trace the path of reflected rays
According to the laws of reflection for spherical mirrors:
Light rays parallel to the principal axis striking a convex mirror diverge after reflection. When these diverged rays are extended backwards, they appear to intersect at a single point behind the mirror called the principal focus ($F$).

Step 3: Determine the image characteristics
1. Nature: Since the reflected light rays do not actually intersect but only appear to diverge from a point behind the mirror, the image formed is virtual.
2. Orientation: Virtual images formed by spherical mirrors are always erect (upright).
3. Size and Position: The image is formed at the principal focus ($F$) behind the mirror and is highly diminished (point-sized).

Thus, when an object is placed at infinity in front of a convex mirror, the nature of the image formed is Virtual and erect.