Which warning plate is correctly mounted?

Answer 1 (“the right one”) is correct because these red/white warning plates must be mounted so that the diagonal stripes “point” outward toward the outer edges of the vehicle or load. From the rear view, that means the stripes on the left side slope down toward the left, and the stripes on the right side slope down toward the right.

Rule of thumb: the stripes should look like an upside-down V across the back, guiding following traffic’s eyes to the outside limits of what is wide/protruding. If they are mounted the other way (stripes slanting inward), they give a misleading impression of the vehicle’s width and the outer edges are less clearly marked.