Select the correct mirror image of the given figure when the mirror is placed along the vertical line MN.

Answer & explanation
Correct answer: option 1
The correct answer is Option (1) →

A mirror on a vertical line turns left into right but keeps top and bottom: every part moves to the opposite side at the same height and faces the other way.

Option (2) — Incorrect. The black triangle is in the correct place but is not turned over: it still faces the same way as in the question figure.
Option (3) — Incorrect. This is the image in a horizontal mirror: the figure is turned upside down instead of left to right.
Option (4) — Incorrect. This is the figure turned through 180° (half a turn): it is flipped both left to right and top to bottom.