Which of the following defines the LUMO?

The definition of the LUMO is the "Lowest Unoccupied Molecular Orbital." This term refers specifically to the molecular orbital that has the lowest energy among those that are unoccupied by electrons in a molecule. Understanding the concept of LUMO is crucial in molecular orbital theory as it plays a significant role in determining a molecule's electronic properties and reactivity.

Molecules will add energy to their systems through various processes, such as photon absorption, promoting electrons from the highest occupied molecular orbital (HOMO) to the LUMO. The energy difference between the HOMO and LUMO is essential for understanding electronic transitions and how a molecule may behave in chemical reactions and interactions.

In contrast, the other options reflect misunderstandings of molecular orbital terminology. The Lowest Occupied Molecular Orbital, for instance, refers to the orbital that is occupied by the highest energy electrons in the ground state of the molecule, and it plays a different role in chemical processes than the LUMO. The other terms mentioned do not accurately describe any recognized definitions in molecular orbital theory. Thus, the clear and precise definition of LUMO as the "Lowest Unoccupied Molecular Orbital" establishes its importance in inorganic chemistry and molecular interactions.