If your image appears to be erect, no matter how far you stand from a mirror, the mirror is likely to be:

Correct — D, Either plane or convex. The phrase that decides this item is 'no matter how far you stand'. Test each surface against it. A plane mirror reflects every object into a virtual image the same size as the object, as far behind the mirror as the object is in front, and always the right way up — the distance you stand makes no difference. A convex mirror bulges towards you, so reflected rays diverge and the image is always virtual, erect and smaller than the object, again for every object position; that is exactly why it is used as a rear-view and blind-corner mirror. A concave mirror is the one that fails the test: it gives an erect, magnified virtual image only while the object lies between the pole and the focus, and as soon as the object moves beyond the focus the image becomes real and inverted. So two of the three surfaces satisfy the condition, and the option that names both is the complete answer.

• (a)Plane — True but incomplete. A plane mirror does always give an erect image, yet so does a convex mirror, and the stem asks what the mirror is likely to be — an option that excludes an equally valid surface is not the best answer.
• (b)Concave — The one surface ruled out. A concave mirror gives an erect virtual image only when the object is closer than the focal point; step back past the focus and the image turns real and inverted.
• (c)Convex — Also true but incomplete, for the same reason as option (a). A convex mirror always gives an erect image, but so does a plane mirror, so naming only one of the two leaves the answer short.

Spherical mirrors are described by the mirror formula, one over v plus one over u equals one over f, with the New Cartesian Sign Convention taking distances from the pole and treating the incident direction as positive. A convex mirror has a virtual focus behind the surface, so for every real object the formula returns a positive image distance — a virtual image — with magnification between zero and one. A concave mirror has a real focus in front, and the sign of the image distance flips as the object crosses that focus, which is why its image changes character with position while the convex mirror's never does.

The trap here is answering the first true option you meet rather than the question actually asked. Options (a) and (c) are both correct statements in isolation; option (d) is the one that satisfies the stem's universal quantifier over distance. Whenever a physics option list contains an 'either A or B' entry alongside A and B separately, test the stem's condition against each surface in turn instead of stopping at the first success. Everyday examples anchor the physics: a bathroom mirror is plane and never inverts you; a vehicle's wing mirror is convex and never inverts you but shrinks everything, hence the warning that objects are closer than they appear; the inside of a polished steel spoon is concave and does invert your face once you hold it far enough away.

• A plane mirror always forms a virtual, erect image of the same size, located as far behind the mirror as the object is in front.
• A convex mirror always forms a virtual, erect and diminished image, for every position of the object.
• A concave mirror forms an erect, magnified virtual image only when the object lies between the pole and the focus; beyond the focus the image is real and inverted.
• Because their field of view is wide and the image is always erect, convex mirrors are used as rear-view mirrors and at blind corners.
• Concave mirrors are used where a beam or a magnified erect image is wanted — vehicle headlights, shaving and dentists' mirrors, and solar concentrators.

• Choosing the first individually true option and missing the compound one that the stem's wording requires.
• Forgetting that a concave mirror is erect for close objects; it is only the far positions that invert.
• Assuming that an erect image must also be the same size; a convex mirror keeps it erect while shrinking it.

As a property-to-mirror identification, as a 'which statement is not true about the image formed by' item, or as a numerical using the mirror formula.

• practice — not a real PYQ

  A convex mirror always forms an image that is which one of the following?

  • (a)Real, inverted and magnified
  • (b)Virtual, erect and diminished
  • (c)Real, erect and of the same size
  • (d)Virtual, inverted and magnified

  Answer(b) Virtual, erect and diminished — true for every position of the object, which is why convex mirrors work as rear-view mirrors.

• practice — not a real PYQ

  A concave mirror forms a virtual and erect image only when the object is placed in which one of the following positions?

  • (a)Beyond the centre of curvature
  • (b)At the centre of curvature
  • (c)Between the pole and the principal focus
  • (d)At infinity

  Answer(c) Between the pole and the principal focus — in every other position the concave mirror gives a real, inverted image.