Question

what is mean by positive , negative, zero overlapping?

Answer 1

The two lobes of a p-orbital are different in phases.One phase is represented by a positive sign,while the other is represented by a negative sign.These two phases can as well be represented by different colors.Thus,a positive overlap is an overlap between orbitals which results when orbitals in the same phases overlap with each other.Bond formation occurs due to positive overlap between orbitals.
A negative phase overlap results when two orbitals with different phase overlap with each other.A zero overlap will results when orbitals do not overlap at all or do not overlap effectively.A zero overlap of orbitals does not result in bond formation.

Answer 2

When the same sign lopes overlap each other is called Positive overlapping

When the different sign lopes overlap each other is called Negative overlapping

When the sign lopes has not overlap each other is called Zero overlapping