How many electrons are present in the second principal energy level (n = 2) of a neutral phosphorus atom?

• A. 5
• B. 3
• C. 2
• D. 8

Answer: (D)

Verified step by step guidance

1. Identify the atomic number of phosphorus, which tells us the total number of electrons in a neutral atom. Phosphorus has an atomic number of 15, so it has 15 electrons.
2. Recall that electrons are arranged in principal energy levels (shells) denoted by the quantum number \(n\). The first principal energy level (\(n=1\)) can hold up to 2 electrons.
3. Determine how many electrons fill the first energy level: since \(n=1\) can hold 2 electrons, subtract these from the total electrons: \$15 - 2 = 13$ electrons remain for higher levels.
4. Next, consider the second principal energy level (\(n=2\)), which can hold a maximum of 8 electrons. Since 13 electrons remain, the \(n=2\) level will be fully occupied with 8 electrons.
5. Therefore, the number of electrons in the second principal energy level (\(n=2\)) of a neutral phosphorus atom is 8.