Which one of the following statements about electrons and atomic orbitals is NOT true according to basic atomic theory?

Introduction / Context:
Atomic orbitals are central to understanding the arrangement of electrons in atoms and the way atoms bond to form molecules. Orbitals differ in shape, size and energy, and electrons fill these orbitals according to several basic rules. This question asks you to identify which statement about electrons and orbitals is not true, which means three of the statements describe accepted ideas and one contradicts basic atomic theory.

Given Data / Assumptions:

• We are dealing with simple quantum mechanical model orbitals such as s, p, d and f.
• Pauli exclusion principle limits the maximum number of electrons in an orbital.
• Aufbau principle and energy levels determine how electrons fill orbitals.
• We focus on ground state electronic configurations in atoms.

Concept / Approach:
Each atomic orbital is a region in space around the nucleus where the probability of finding an electron is high. An orbital can hold at most two electrons and these must have opposite spins. Different orbitals have different energies; for example, a 1s electron is lower in energy than a 2s electron. Electrons generally occupy the lowest available energy orbitals first. Because of these ideas, any statement claiming that electrons have the same energy in all orbitals must be false. The other statements reflect standard features of atomic orbitals and electron filling rules.

Step-by-Step Solution:
Step 1: Examine option A. It says that a single orbital can hold a maximum of two electrons with opposite spins. This matches the Pauli exclusion principle and is true. Step 2: Examine option C. It states that the lowest energy level of an atom consists of a single s orbital. The n = 1 shell has only the 1s orbital, so this is also true. Step 3: Examine option D. It describes the idea that electrons fill lower energy orbitals before higher ones, which is the Aufbau principle and is true. Step 4: Examine option E. It defines orbitals as regions of space where electrons are most likely to be found, which is the standard probabilistic interpretation of orbitals and is true. Step 5: Examine option B. It claims that an electron has the same energy in all orbitals. This contradicts the known fact that energy levels differ between shells and subshells, so this statement is not true.

Verification / Alternative check:
You can verify the incorrectness of option B by recalling that spectral lines of hydrogen and other elements arise because electrons move between orbitals of different energy. The energy difference between levels corresponds to specific photon wavelengths. Additionally, electron configuration notation such as 1s2 2s2 2p6 shows that electrons occupy orbitals with increasing energy. If all orbitals had the same energy, there would be no reason for them to fill in a particular order and no spectral lines would exist. The existence of distinct shells and subshells in atomic structure proves that option B cannot be correct.

Why Other Options Are Wrong as the NOT true choice:
- A single atomic orbital can hold a maximum of two electrons with opposite spins: This is a standard rule and is true, so it cannot be the incorrect statement asked for.
- The lowest energy level of an atom consists of a single s orbital: For n = 1, only the 1s orbital exists, so this statement is true.
- Electrons fill lower energy orbitals before occupying higher energy ones: This is the basis of the Aufbau principle and matches observed ground state configurations.
- Orbitals represent regions of space where an electron is most likely to be found: This is the accepted probabilistic definition of orbitals and is correct.

Common Pitfalls:
Students sometimes confuse orbitals with shells or think that all orbitals in the same shell have identical energy in multi electron atoms, which is not always the case. Another common confusion is between Bohr model orbits and quantum mechanical orbitals. Remember that different orbitals have characteristic shapes and energies, and that electron configurations are built by filling the lowest energy orbitals first. Any statement that ignores these energy differences or suggests that all orbitals are equivalent in energy should be treated with suspicion.

Final Answer:
The statement that is NOT true is An electron always has the same energy no matter which orbital it occupies.