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TNPSC chemistry practice questions: atoms, elements and the periodic table

By the PrepMatic team · Updated 9 Oct 2026 · 3 min read

Chemistry in the TNPSC General Studies paper is school-level and fact-driven. The first block, atoms and elements, is where you learn the vocabulary that the rest of the subject uses: atomic number, valency, isotopes, mixtures and compounds. With General Science at about 5 of the 75 questions in the paper, expect one chemistry question at most from this block, but a miss costs the same as a miss elsewhere. The five questions below cover the commonest types. TNPSC General Science covers the subject in full.

What this topic covers

• Atomic structure: protons, neutrons and electrons, and who discovered each.
• The periodic table: the modern periodic law, groups and periods, and noble gases.
• Valency and bonding: how the outer shell decides how an element combines.
• Matter: elements, compounds and mixtures, and how to separate mixtures.

The atomic number is the number of protons. The mass number is the number of protons plus neutrons.

Sample questions

Question 1

In the modern periodic table, the elements are arranged in increasing order of their:

• A. atomic mass
• B. density
• C. number of neutrons
• D. atomic number

Question 2

The valency of sodium (atomic number 11) is:

• A. 1
• B. 2
• C. 3
• D. 8

Question 3

Which of the following is a noble gas?

• A. Nitrogen
• B. Hydrogen
• C. Neon
• D. Oxygen

Question 4

Which of the following is a mixture?

• A. Distilled water
• B. Air
• C. Sodium chloride
• D. Carbon dioxide

Question 5

Isotopes of an element have the same number of:

• A. protons
• B. neutrons
• C. mass numbers
• D. physical properties

Answers and explanations

1. D. The modern periodic law says that the properties of elements are a periodic function of their atomic number. Mendeleev's older table used atomic mass.
2. A. Sodium has the electron arrangement 2, 8, 1. It has one electron in the outer shell, which it readily gives up, so its valency is 1.
3. C. Neon belongs to Group 18, the noble gases, which have full outer shells and are very unreactive. Nitrogen, hydrogen and oxygen are reactive non-metals.
4. B. Air is a mixture of gases, mainly nitrogen and oxygen, in no fixed ratio. Distilled water, sodium chloride and carbon dioxide are pure compounds.
5. A. Isotopes are atoms of the same element, so they have the same number of protons, but different numbers of neutrons, which gives them different mass numbers and slightly different physical properties.

How to prepare atoms and elements

Start with the first twenty elements: names, symbols, atomic numbers and electron arrangements. This small set covers valency, group and period questions. Write them in a table, hide a column, and recite the hidden column. Ten minutes a day for a week is enough.

Learn a handful of group names that the paper likes: alkali metals (Group 1), alkaline earth metals (Group 2), halogens (Group 17) and noble gases (Group 18). Add the common compounds and their formulae (water H₂O, common salt NaCl, carbon dioxide CO₂, ammonia NH₃) because they turn up in everyday-chemistry questions.

Separate three ideas that students often blur: an element has one kind of atom, a compound has two or more elements chemically joined in a fixed ratio, and a mixture is a physical combination in variable proportion. Examples help: oxygen (element), water (compound), air (mixture).

Continue to TNPSC chemistry: acids, bases and metals practice for the second chemistry block.

Take the full topic test on PrepMatic

A short PrepMatic topic test (about 15 questions, 30 minutes) will show whether the chemistry basics have stuck. Because General Science is only a small unit, take the test once after finishing the unit and once more a week before your exam. If you want to practise in Tamil, choose Tamil as your exam language in your account.

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