Chemistry: Physical Chemistry: UPSC Previous Year Questions (Science and Technology)
4 previous year UPSC Prelims questions on Chemistry: Physical Chemistry (Science and Technology). Choose an option to see the answer and explanation.
Explanations state facts as of the year each question was asked; words like “recently” refer to that year.
Showing 1–4 of 4 questions
UPSC 2001Science and Technology · Chemistry: Physical Chemistry
Q1. In an atom, the order of filling up of the orbitals is governed by:
Explanation
The order of filling up orbitals in an atom is governed by Aufbau’s principle, which states that electrons occupy orbitals in order of increasing energy levels, starting from the lowest energy orbital first. The sequence is determined by the (n + l) rule, where n is the principal quantum number and l is the azimuthal quantum number. If two orbitals have the same (n + l) value, the orbital with the lower n value is filled first.
UPSC 2001Science and Technology · Chemistry: Physical Chemistry
Q2. A radioactive substance has a half-life of four months. Three-fourth of the substance would decay in:
Explanation
The half-life of a radioactive substance is the time it takes for half of the substance to decay. After each half-life:
At the end of 1 half-life (4 months), 50% of the substance remains. At the end of 2 half-lives (8 months), 25% of the substance remains, meaning 75% (three-fourths) of the substance has decayed. Thus, it takes 8 months for three-fourths of the substance to decay.
UPSC 2001Science and Technology · Chemistry: Physical Chemistry
Q3. Which one of the following is NOT radioactive?
Explanation
Astatine, Francium, and Tritium are radioactive elements:
Astatine is a halogen with no stable isotopes.
Francium is an alkali metal, highly unstable and radioactive. Tritium is a radioactive isotope of hydrogen. Zirconium is not radioactive. It is a stable, non-radioactive metal widely used in industries like nuclear reactors and construction.
UPSC 2001Science and Technology · Chemistry: Physical Chemistry
Q4. Match List I with List II and select the correct answer using the codes given below the lists:
List-I (Characteristic)
List-II (Particle)
A. Zero mass
1. Positron
B. Fractional charge
2. Neutrino
C. Fractional spin
3. Quark
D. Integral spin
4. Photon
Explanation
A is matched with 2: Neutrino is a particle with almost zero mass and no electric charge, making it the correct match for zero mass. B is matched with 3: Quarks are fundamental particles with fractional charges, such as +2/3 or -1/3. C is matched with 1: Positrons, the antimatter counterparts of electrons, possess fractional spin, matching this characteristic. D is matched with 4: Photons are elementary particles of light with an integral spin of 1, classifying them as bosons. Direction: The following item consists of two statements. One labeled as the ‘Assertion (A)’ and the other as "Reason (R). You have to answer this item using the code given below: (2000)
Answer key for these questions
Q
UPSC year
Correct answer
1
2001
(a) Aufbau’s principle
2
2001
(c) 8 months
3
2001
(d) Zirconium
4
2001
(a) A-2; B-3; C-1; D-4
Frequently asked questions
How many previous year UPSC questions are there on Chemistry: Physical Chemistry?
This page covers 4 previous year UPSC Prelims GS Paper-I questions on Chemistry: Physical Chemistry (Science and Technology), asked from 1996 to 2009. Each has the correct answer and an explanation.
How should I use previous year UPSC questions for Prelims?
Attempt each question first, then open the answer and read the explanation for every option. Repeat by chapter, and track which statements UPSC reuses across years. Previous year questions show the exam pattern and difficulty level.
Which years are covered for Chemistry: Physical Chemistry?
Questions on Chemistry: Physical Chemistry (Science and Technology) are available for 8 years, from 1996 to 2009. Use the Year filter to practise a single paper.
