Question

why are the two mirrors in a periscope placed paralled ?

Answer 1

to see the image of anything
parallel mirrors reflect each other
that's we can see the image

Answer 2

The two mirrors in a periscope are placed paralleled with an angle of 45 degrees to the corner of it so as to allow the reflection of light and helps in vision. A periscope is used for looking over the heads of crowd and to see the image of any object.
Hope it will help you.
MARK IT AS BRAINLIEST please :-) *