determine which of the following electron configurations are not valid:\n16) 1s²2s²2p⁶3s²3p⁶4s²4d¹⁰4p⁵\n17)…

Explanation:

Step1: Analyze electron configuration rules

Electron configurations must follow the Aufbau principle (filling orbitals in order of increasing energy), Pauli exclusion principle (each orbital can hold at most 2 electrons with opposite spins), and Hund's rule (electrons occupy degenerate orbitals singly before pairing). Also, orbital capacities: (s) - 2 electrons, (p) - 6 electrons, (d) - 10 electrons, (f) - 14 electrons.

Step2: Check each configuration

• 16) (1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}4d^{10}4p^{5}): After (4s), it should be (3d) before (4p) (Aufbau principle violation).
• 17) (1s^{2}2s^{2}2p^{6}3s^{3}3d^{5}): (3s) can hold at most 2 electrons (Pauli exclusion principle violation).
• 18) ([Ra]7s^{2}5f^{8}): (Ra) is in period 7, but (5f) is filled after (6d) (Aufbau principle violation).
• 19) ([Kr]5s^{2}4d^{10}5p^{5}): Follows Aufbau, Pauli, and Hund's rules.
• 20) ([Xe]): Incomplete (no valence - shell electrons specified).

Answer:

16. Invalid (Aufbau principle violation).
17. Invalid (Pauli exclusion principle violation).
18. Invalid (Aufbau principle violation).
19. Valid.
20. Invalid (incomplete).