Assertion: Electric flux density is independent of medium.

Reason: It depends only on distance and charge.

Assertion: For a charged shell, potential inside shell depends only on the field inside shell.

Reason: Potential of shell may be determined only by the field outside.

Assertion :- Electrostatic energy does not follow superposition principle. 

Reason :- Electrostatic energy density is a quadratic function.

Assertion: We cannot find electric field from Gauss's law for unsymmetrical charge distribution.

Reason: Gauss's law is not applicable for unsymmetrical charge distribution.