Final answer:
Electrons with a lower principal quantum number are on average closer to the nucleus. Electrons are more tightly bound and have lower energy at lower quantum numbers, also experiencing a higher effective nuclear charge.
Step-by-step explanation:
The electron that is on average closer to the nucleus can be identified using the principal quantum number (n). Electrons with a lower principal quantum number (n=1,2,3...) are found closer to the nucleus, where they experience a strong attractive force from the positively charged nucleus. As n decreases, electrons are more tightly bound and thus, closer to the nucleus, indicating a lower and more negative energy state, which corresponds to the ground state.
Electron configurations with higher values of n represent electrons that are, on average, further from the nucleus and are less tightly bound, making them easier to remove from the atom. The effective nuclear charge (Zeff) also plays a role; electrons closer to the nucleus experience Zeff more closely to the full nuclear charge, resulting in a stronger attraction.