Which of the following ranks the orbitals 1s, 2s, and 3s in order of increasing size?

• A. 1s < 3s < 2s
• B. 3s < 2s < 1s
• C. 2s < 1s < 3s
• D. 1s < 2s < 3s

Answer: (D)

Verified step by step guidance

1. Understand that the size of an orbital generally increases with the principal quantum number \( n \). The principal quantum number \( n \) indicates the energy level and relative size of the orbital.
2. Recall that the 1s orbital has \( n = 1 \), the 2s orbital has \( n = 2 \), and the 3s orbital has \( n = 3 \). Orbitals with higher \( n \) values are larger because the electron is, on average, farther from the nucleus.
3. Compare the orbitals based on their principal quantum numbers: since \( 1 < 2 < 3 \), the size of the orbitals increases in the order \( 1s < 2s < 3s \).
4. Note that the shape of the orbitals (all are s orbitals, which are spherical) remains the same, so the size difference is primarily due to the energy level \( n \).
5. Conclude that the correct ranking of the orbitals in order of increasing size is \( 1s < 2s < 3s \).