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UPSC 2001: In an atom, the order of filling up of the orbitals is governed by
(a)Aufbau principle
(b)Heisenberg’s uncertainty principle
(c)Hund’s rule
(d)Pauli’s exclusion principle
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Not attemptedCorrect Answer: (a) Aufbau principle
The order in which orbitals are occupied (1s→2s→2p→3s, etc.) is specified by the Aufbau principle, which arranges orbitals in increasing (n + l) energy. The other listed principles deal with uncertainty (Heisenberg), maximum multiplicity (Hund) and spin pairing limits (Pauli) and do not set the filling order. ([edurev.in](https://edurev.in/t/203065/Chemistry-Solved-Questions--1995-2020--1?utm_source=openai))
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Frequently Asked Questions
What is the correct answer to this UPSC 2001 Science & Technology question?▼
The correct answer is option (a): Aufbau principle. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Chemistry question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2001, GS Paper 1, as Question 119. It falls under Science & Technology > Chemistry.
What is the difficulty level of this UPSC question?▼
This question is rated "easy". It tests basic recall and most well-prepared aspirants should answer it correctly.
How many UPSC Prelims questions have been asked from Chemistry?▼
UPSC has asked 53 questions from Chemistry (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.