A solid sphere of radius $$R$$ carries a positive charge $$Q$$ distributed uniformly throughout its volume. A very thin hole is drilled through it's centre. A particle of mass $$m$$ and charge $$-$$q performs simple harmonic motion about the centre of the sphere in this hole. The frequency of oscillation is

Assertion (A) In a region of constant potential, the electric field is zero and there can be no charge inside the region.

Reason (R) According to Gauss law, charge inside the region should be zero if electric field is zero.

Statement (A) Inside a charged hollow metal sphere, $$E=0, V \neq 0$$, (where, $$E=$$ electric field, $$V=$$ electric potential).

Statement (B) The work done in moving a positive charge on an equipotential surface is zero.

Statement (C) When two like charges are brought closer, their mutual electrostatic potential energy will increase.

Electrostatic force between two identical charges placed in vacuum at distance of $$r$$ is F. A slab of width $$\frac{r}{5}$$ and dielectric constant 9 is inserted between these two charges, then the force between the charges is