Which of the following configurations is incorrect?

Which of the following configurations is incorrect?

Step 1: Understand that electron configurations show how electrons are arranged in an atom.
Step 2: Know that each shell (energy level) can hold a maximum number of electrons: 1st shell can hold 2, 2nd shell can hold 8, and 3rd shell can hold 18.
Step 3: Look at the given configuration: 1s2 2s2 2p6 3s2 3p6.
Step 4: Count the electrons in each shell: 1s2 has 2, 2s2 has 2, 2p6 has 6, 3s2 has 2, and 3p6 has 6.
Step 5: Add the electrons in the 3rd shell: 3s2 (2 electrons) + 3p6 (6 electrons) = 8 electrons in the 3rd shell.
Step 6: Compare the total in the 3rd shell (8 electrons) to the maximum allowed (18 electrons). This is correct.
Step 7: However, the total number of electrons in the configuration is 2 + 2 + 6 + 2 + 6 = 18, which is fine, but the 3rd shell can only hold 8 in this context.
Step 8: Conclude that the configuration is incorrect because it suggests more electrons in the 3rd shell than allowed.

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