Can a plane mirror be called a spherical mirror?

The ray diagram given below illustrates the experimental setup for the determination of the focal length of a converging lens using a plane mirror.
$(i)$ State the magnification of the image formed.
$(ii)$ Write two characteristics of the image formed.
$(iii)$ What is the name given to the distance between the object and the optical centre of the lens in the given diagram?

$A$ concave lens made of a material of refractive index $n_{1}$ is kept in a medium of refractive index $n_{2}$. $A$ parallel beam of light is incident on the lens. Complete the path of rays of light emerging from the concave lens if
$(i)$ $n_{1} > n_{2}$ $(ii)$ $n_{1}=n_{2}$ $(iii)$ $n_{1} < n_{2}$

What is the ratio of the velocity of light in a transparent medium with a refractive index of $1.5$ to the velocity of light in a vacuum?

What is the focal length of a plane mirror?

The image formed by a convex mirror is only one-third of the size of the object. If the focal length of the mirror is $12 \, cm$,the image formed will be