Select the correct mirror image of the given figure when the mirror is placed at MN as shown below.

Correct — B. MN is the vertical line standing to the right of the strip, so the image is a lateral inversion.

Rule: reverse the reading order, then flip every single character left to right.

The strip reads T p 6 9 a q, so the mirror runs q a 9 6 p T with each shape inverted — the q turns into a p, the p turns into a q, and the T is unaltered because it is symmetric about a vertical axis.

The digits are the test. A mirrored 6 keeps its loop at the bottom with the arc swinging to the left, and a mirrored 9 keeps its loop at the top with the tail on the left.

Option (b) carries all six inversions, both digits included.

Why the others are wrong

• (a)
  The order is reversed but the fourth character is printed as an upright 9, and the a is turned upside down rather than flipped sideways. A vertical mirror never rotates a character.
• (c)
  The two digits are printed as an ordinary 6 and 9, un-inverted, and the strip opens with q where the mirror of the final q has to be a p.
• (d)
  Five characters are inverted correctly, but the T stands on its head with the crossbar at the bottom. That is a water image, which a mirror on a vertical line cannot produce.

A mirror on a vertical line does two things at once, and candidates usually do only one of them.

First the reading order reverses: the character nearest the mirror becomes the leftmost character of the image.

Second each glyph is flipped about its own vertical axis, so b and d swap, p and q swap, and 6 and 9 turn into shapes that are not ordinary digits.

Characters symmetric about a vertical axis — A, H, I, M, O, T, U, V, W, X, Y, 0 and 8 — come through unchanged, which is why they eliminate nothing on their own.

Key facts

• A mirror on a vertical line reverses the reading order and flips each character left to right.
• Capitals symmetric about a vertical axis include A, H, I, M, O, T, U, V, W, X and Y.
• The digits 0 and 8 survive a vertical mirror unchanged, while 6 and 9 do not.
• A character turned upside down belongs to a water image, which is a mirror on a horizontal line.

Common traps

• Reversing the order but leaving the individual glyphs unflipped.
• Accepting an option because its first and last characters look right, without checking the digits.
• Confusing an upside-down character with a laterally inverted one.

No directly related past PYQ was found.