Question

if displacement of a particle is 0 then what is its distance

Answer 1

If the displacement of the particle is zero then it is not necessary that its distance also must be zero.
Distance is the total length covered while displacement is the shortest distance between initial and final point .

If displacement is zero then it's distance may be positive or 0.

Answer 2

The distance may or may not be zero. It will not be zero if the particle comes back to its initial position after traveling some distance. But in that case displacement will be zero. For example, this happens in a circular path.