Question

which of the following is not a dielectric?
a) ebonite
b)mica
c)water
d)oil
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Answer 1

ebonite is a answer in this question

Answer 2

Dielectric

c)water

Dielectrics are insulators that can be polarized, this means when dielectrics are placed in an electric field then practically no current will flow through it but phenomenon of electric polarization takes place , it has the ability to transmit electric force without conduction  and it reduces the electric field within dielectric.

We know that water is a good conductor of electricity, hence tap water can't be dielectric.