Three of the panels show this green block in a mirror placed somewhere around it (upright, flat or slanting). Which panel is NOT a mirror image?

A mirror image always reverses the turning sense of the figure. (a), (b) and (d) are reflections in an upright, a flat and a slanting mirror. (c) is only the block turned through a quarter-turn, which keeps the turning sense, so no mirror can produce it.