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The principal quantum number is represented by the symbol "n" in the context of quantum mechanics. This quantum number indicates the main energy level or shell in which an electron resides in an atom.
Here's how the principal quantum number relates to the characteristics listed in the question:
1. **Orbital Size**: The principal quantum number determines the average distance of an electron from the nucleus. As the principal quantum number increases, the average distance of the electron from the nucleus also increases, indicating larger orbital sizes for electrons in higher energy levels.
2. **Orbital Mass**: The principal quantum number does not directly relate to orbital mass. Orbital mass is not a characteristic given by the principal quantum number.
3. **Orbital Shape**: The shape of an orbital (s, p, d, f) is determined by the values of the other quantum numbers (l, m_l). The principal quantum number contributes to the energy of the orbital but does not define its shape.
4. **Orbital Orientation**: The orientation of an orbital in space is determined by the magnetic quantum number (m_l), which is related to the principal quantum number but does not solely depend on it. The principal quantum number alone does not provide information about the specific orientation of an orbital.
Therefore, the characteristic given by the principal quantum number from the options provided is **orbital size**. It influences the average distance of an electron from the nucleus and, consequently, the size of the orbital in which the electron is located.
