In the case of concave mirror the light ray passing through centre of curvature, after reflection

Light ray passing through the centre of curvature of concave mirror

retraces its path, because as the ray of light passes through the centre of

curvature of a concave mirror at$\text{90°}$ . Hence the incident ray coincides with

normal

$\text{Li}=\text{Lr}$

$\text{Li}=0$

$\text{Lr}=0$

So the ray of light retraces it’s path