Question

why is the image formed in a periscope is virtual without lateral inversion?

Answer 1

Periscope is made of two plane mirrors and the image formed by a plane mirror is called a virtual image because it is formed where the virtual rays appear to come from when the real rays are reflected by the mirror.
The final image produced by the periscope is without lateral inversion. This is because the light rays from the object are reflected by two mirrors, so the lateral inversion caused by the first mirror is reversed by the second mirror.