Enilist the favourable conditions for orbital overlap.

Answer

### Step-by-Step Solution:

1. **Condition of Electron Presence**:
- The atomic orbitals involved in the overlap must contain at least one electron. This means that for effective overlap, the orbitals should be half-filled or fully filled. This allows for the formation of bonds through the sharing of electrons.

2. **Opposite Spins of Electrons**:
- When two atomic orbitals overlap, the electrons in these orbitals must have opposite spins. This is crucial because according to the Pauli Exclusion Principle, no two electrons in an atom can have the same set of quantum numbers. Therefore, having opposite spins allows for the pairing of electrons, which is essential for bond formation.

3. **Similar Energy Levels**:
- The combining atomic orbitals should have the same or nearly the same energy levels. For example, in a homonuclear diatomic molecule, the 1s orbital of one atom can effectively overlap with the 1s orbital of another atom, but it cannot overlap with a 2s orbital due to the significant difference in energy levels.

4. **Maximum Overlap**:
- The extent of overlap between the atomic orbitals should be maximized. Greater overlap leads to stronger bonds. This means that the orientation and distance between the overlapping orbitals should be such that they can achieve the greatest possible overlap.

### Summary of Favorable Conditions for Orbital Overlap:
1. Atomic orbitals must contain at least one electron (half-filled or fully filled).
2. Electrons in the combining orbitals must have opposite spins.
3. The atomic orbitals should have similar or nearly similar energy levels.
4. The overlap between the orbitals should be maximized for stronger bonding.