Question

What will happen to the focus when a spherical mirror is kept in a water ?

Answer 1

the focus will be deflected and the point of focus will be further due to refraction of light

Answer 2

Mirrors, spherical or otherwise, operate on the principle that the angle of reflection of a ray of light equals the angle at which it strikes the mirror's surface. That behavior is not affected by the medium in which the light travels, so the mirror's focal length would be no different in air or water.