Question:
Which of the following is correct set of 4 quantum numbers of 19th electron in Chromium (Atomic number = 24) in accordance with Aufbau principle?
Which of the following is correct set of 4 quantum numbers of 19th electron in Chromium (Atomic number = 24) in accordance with Aufbau principle?
Updated On: Apr 10, 2026
- \(n=3, l=2, m=+2, s=+\frac{1}{2}\)
- \(n=3, l=2, m=-2, s=+\frac{1}{2}\)
- \(n=4, l=1, m=0, s=+\frac{1}{2}\)
- \(n=4, l=0, m=0, s=+\frac{1}{2}\)
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
The Aufbau principle states that electrons fill orbitals in order of increasing energy. The order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, etc. We must count to the 19th electron following this sequence.
Step 2: Key Formula or Approach:
1. Electron 1-2: 1s orbital 2. Electron 3-4: 2s orbital 3. Electron 5-10: 2p orbitals 4. Electron 11-12: 3s orbital 5. Electron 13-18: 3p orbitals (Ar configuration) 6. Electron 19: 4s orbital (starts the K shell/4th period)
Step 3: Detailed Explanation:
1. The 18th electron completes the \(3p\) subshell. 2. According to the \((n+l)\) rule, the next orbital to be filled is \(4s\) (\(n=4, l=0\)), because \(4+0=4\) is less than \(3+2=5\) (for \(3d\)). 3. Therefore, the 19th electron enters the \(4s\) orbital. 4. Quantum numbers for 4s: \(n=4\), \(l=0\), \(m=0\), \(s=+1/2\).
Step 4: Final Answer:
The correct set is \(n=4, l=0, m=0, s=+\frac{1}{2}\).
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