What is the principal focus of a spherical mirror?

It is a point from which the rays of light appear to be coming from onthe principal axis of
a convex mirror.

It is the point on theprincipal axis through whichraysof light parallel to the principal axis
pass after reflection or appear to be arising from this point on the principal axis.

It is the centre of a hollow sphere of which the spherical mirroris a part.

It is the midpoint of a spherical mirror.