During the formation of a molecular orbital from atomic orbitals, the probability of electron density is zero in the nodal plane.

Explanation:
- Molecular orbitals are formed by the combination of atomic orbitals from different atoms in a molecule.
- Atomic orbitals are regions of space where there is a high probability of finding an electron.
- When atomic orbitals combine to form molecular orbitals, there are regions of space where the probability of finding an electron is either increased or decreased compared to the individual atomic orbitals.
- These regions are called nodal planes, which are areas in the molecular orbital where the wave functions of the atomic orbitals cancel each other out, resulting in zero probability of finding an electron.
- In other words, the electron density is zero in the nodal plane.
- The nodal plane is a planar region that passes through the nuclei of the atoms involved in the molecular orbital formation.
- The number of nodal planes in a molecular orbital depends on the type of molecular orbital and the combination of atomic orbitals involved.
- For example, in a sigma bonding molecular orbital formed by the overlap of two s atomic orbitals, there is a single nodal plane passing through the nuclei of the atoms.
- In a pi bonding molecular orbital formed by the overlap of two p atomic orbitals, there is a nodal plane passing through the nuclei perpendicular to the internuclear axis.
- The presence of nodal planes affects the electron density distribution in the molecular orbital, resulting in regions of high electron density (lobes) and regions of zero electron density (nodal planes).

In conclusion, during the formation of a molecular orbital, the probability of electron density is zero in the nodal plane, which is a planar region where the wave functions of the atomic orbitals cancel each other out.