Question

How are two mirrors placed in a periscope?1Parallel to each other 2 Perpendicular to each other 3 Making angle 45° with each other 4 Making angle 60° with each other

Answer 1

Periscope is an optical instrument which is used to observe what is going on the surface of water in the submarines.
It is also used for observation purpose in trenches of world war.

Principle of working:
Reflection of light.

In simple periscope, two mirrors are placed at an angle 45 degrees.

Working principle:
Parallel rays fom distant object fall on first mirror and gets reflected at same angle and they are made to incident second mirror and again parallel rays are reflected to our eyes by which we can see.

Answer 2

A periscope is an optical instrument used to view object which is not in direct sight of human eye. It works by using the Laws of Reflection and are widely used in submarines to navigate under water. 
It works by using two mirrors placed at angle of 45 degree with each other. When light falls on one mirror, it bounces to the other mirror and then reaches the human eye.
A simple periscope only uses mirrors but complex periscope uses prisms instead of mirror. These periscopes are used in the field of medicine particularly in cystoscopy and endoscopy.