The correct answer is option 3, which is a plane mirror. A periscope is an optical device that allows the viewer to see objects without being directly in line of sight. It is commonly used in submarines, military applications, and even in some cameras.
A plane mirror, also known as a flat mirror, is a mirror with a flat reflective surface. It reflects light in a way that preserves the image of the object being reflected. In a periscope, the use of plane mirrors allows the light to be reflected multiple times to enable the viewer to see objects that would otherwise be obstructed.
Concave lenses and concave mirrors, which are options 1 and 2 respectively, have a different shape and optical properties. A concave lens is thinner at the center and thicker at the edges, causing light rays to diverge. A concave mirror, on the other hand, is curved inward and focuses light rays to a point.
Therefore, a plane mirror is the correct option for making a periscope as it allows the reflection of light at different angles, enabling the viewer to see objects from a different position without being in direct line of sight.