An insulated non-conducting solid sphere of radius $$a$$, carrying a positive charge $$+4Q$$ uniformly distributed throughout its volume, is surrounded by a concentric thick conducting spherical shell of inner radius $$b$$ and outer radius $$c$$. This thick shell carries a negative charge $$-2Q$$, see figure. The correct option or options is or are

A

Electric field strength at distance $$r$$, with $$r < a$$, from the center is $$\vec E = \frac{1}{4\pi\epsilon_0}\frac{4Q}{a^3}\vec r$$

B

Charge on the inner surface of the conducting spherical shell is $$+2Q$$

C

Charge on the outer surface of the conducting spherical shell is $$+2Q$$

D

Electrical energy stored in region $$0 < r < a$$, that is in the inner sphere, is $$\frac{2Q^2}{5\pi\epsilon_0a}$$