When a boy stands at various distances in front of a mirror, his image remains erect at all times. Which mirror it must be?

• A concave mirror forms real and inverted or virtual and erect images depending on the distance between the object and the mirror.
• A convex mirror always forms a virtual, diminished and erect image irrespective of the distance between the object and the mirror.
• A plane mirror always forms a virtual, erect and same-size image irrespective of the object distance.

Since the image of the boy is erect at all times, it could be a convex mirror or a plane mirror.