Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Zero orbital overlap is an out of phase overlap.
Reason R: It results due to different orientation/direction of approach of orbitals.
In the light of the above statements, choose the correct answer from the options given below

We are given the following statements:

Assertion A: Zero orbital overlap is an out of phase overlap.

Reason R: It results due to different orientation/direction of approach of orbitals.

When two atomic orbitals approach each other, they can overlap in three ways: positive overlap (in-phase, leading to bonding), negative overlap (out-of-phase, leading to antibonding), and zero overlap. Zero overlap occurs when the positive and negative contributions to the overlap integral cancel each other out exactly, giving a net overlap of zero.

This zero overlap is indeed classified as an out-of-phase overlap because the regions of constructive overlap are exactly cancelled by regions of destructive overlap. For instance, when a $$p_x$$ orbital approaches an $$s$$ orbital along the y-axis, the positive lobe of the p-orbital overlaps with the s-orbital constructively on one side, while the negative lobe overlaps destructively on the other side, resulting in net zero overlap.

The reason this happens is precisely because of the orientation or direction of approach of the orbitals. When orbitals approach in a direction where their symmetries do not match for effective overlap, the result is zero net overlap. So Reason R correctly explains why zero overlap (an out-of-phase overlap) occurs.

Hence, both Assertion A and Reason R are true, and R is the correct explanation of A. The correct answer is Option A.