Assertion : In the absence of an externally applied electric field, the displacement per unit volume of a polar dielectric material is always zero.
Reason : In polar dielectrics, each molecule has a permanent dipole moment but these are randomly oriented in the absence of an externally applied electric field.
Answer & explanation
Correct answer: option 2
D= εoE+ P
vector E = applied electric field and vector P = polarisation or dipole moment per unit volume.
Now in the absence of an electric field (vector E = 0) the polarisation vector P vanishes (because vector p is there if vector E is there).
Therefore displacement vector D = 0