Q.Two plane mirrors are inclined at angle 40° between them. Number of images seen of a tiny object kept between them is (A) Only 8 (B) Only 9 (C) 8 or 9 (D) 9 or 10

A single plane mirror always forms a virtual, laterally-inverted image of exactly the same size as the object, positioned at exactly the same perpendicular distance behind the mirror as the object is in front of it -- true whether the reflecting surface is an actual mirror or a still body of water. When an object is placed between TWO plane mirrors inclined to each other at angle $\theta$ (as in a kaleidoscope), repeated reflection between the two surfaces produces MULTIPLE images, with the exact count depending both on $\theta$ and on precisely where the object sits. Defining $n=\frac{360^\circ}{\theta}$, and $N$ as the number of images: if $n$ is an EVEN integer, $N=n-1$ regardless of object position; if $n$ is an ODD integer and the object sits exactly on the angle bisector, $N=n-1$; if $n$ is an odd integer but the object is OFF the bisector, $N=n$; and if $n$ is not an integer at all, $N$ equals its integer part.

This four-case rule means the same physical angle can give a DIFFERENT image count depending purely on where within that angle the object is placed (relevant only when $n$ works out to an odd integer) -- a subtlety often missed, since for most angles $n$ is not a whole number and only the fourth, simplest rule (take the integer part) applies.