An object is placed symmetrically between two plane mirrors, inclined at an angle of ${72}^{\circ }$, then the total number of images observed is

The correct option is B $4$
For number of images formed using two inclined plane mirrors
$m=\frac{360}{\theta }=\frac{360}{72}=5$

If it was at any other point the number of images $\left(n\right)=m$ but since it is placed symmetrically:
$n=m-1$
or $n=5-1$
or $n=4$ images