The correct answer for the question is option 2: convex.

Rear-view mirrors in vehicles are designed to provide a wider field of view for the driver while minimizing distortion. Convex mirrors are specifically used for this purpose.

A convex mirror is curved outward, meaning it bulges outwards from the center. This curvature causes light to spread out as it reflects off the mirror`s surface. As a result, the reflected image appears smaller and wider than it actually is, but it provides a much wider field of view compared to a flat mirror. This is particularly useful for rear-view mirrors in vehicles as it allows the driver to see a larger area behind the vehicle without having to turn their head.

On the other hand, concave mirrors are curved inward, meaning they cave inwards towards the center. This curvature causes light to converge, resulting in a magnified and focused image. Concave mirrors are commonly used in applications such as telescopes and shaving mirrors, but they are not suitable for rear-view mirrors in vehicles as they provide a narrow field of view.

Therefore, option 2 (convex) is the correct answer for this question.