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TNPSC chemistry practice questions: acids, bases, metals and salts

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

Acids, bases, metals and salts are the second half of school chemistry and the part that appears most in TNPSC papers, because the topics are everyday: lemon juice, rust, baking soda, vinegar. The General Science unit has about 5 of the 75 questions, so a good grasp of this chapter can win you a mark or two with little effort. The five questions below follow the common patterns. For the whole subject, see TNPSC General Science.

What this topic covers

• Acids and bases: properties, indicators and the pH scale.
• Natural sources of acids: the acid in citrus fruit, tamarind, curd and vinegar.
• Metals and non-metals: properties, the reactivity series, corrosion.
• Salts and common compounds: baking soda, washing soda, bleaching powder, plaster of Paris.

On the pH scale, 7 is neutral, values below 7 are acidic and values above 7 are basic. Blue litmus turns red in acid, and red litmus turns blue in base.

Sample questions

Question 1

A solution has a pH of 3. The solution is:

• A. strongly basic
• B. neutral
• C. acidic
• D. weakly basic

Question 2

Which pair of acid and source is NOT correctly matched?

• A. Lemon: citric acid
• B. Tamarind: tartaric acid
• C. Curd: lactic acid
• D. Vinegar: formic acid

Question 3

Which metal is liquid at room temperature?

• A. Sodium
• B. Mercury
• C. Aluminium
• D. Iron

Question 4

Rusting of iron needs:

• A. both oxygen and moisture
• B. only oxygen
• C. only water
• D. nitrogen and carbon dioxide

Question 5

The chemical name of baking soda is:

• A. sodium carbonate
• B. sodium hydrogencarbonate
• C. sodium chloride
• D. calcium carbonate

Answers and explanations

1. C. A pH below 7 means an acidic solution, and a pH of 3 is fairly strongly acidic. A neutral solution has a pH of 7 and basic solutions are above 7.
2. D. Vinegar contains acetic acid, not formic acid. Formic acid is the acid in ant stings and nettle leaves.
3. B. Mercury is the only common metal that is liquid at room temperature. It is used in thermometers and some barometers. Sodium, aluminium and iron are solids.
4. A. Iron rusts when it is in contact with both oxygen and water or moist air. Painting, oiling, galvanising (coating with zinc) and alloying prevent rusting.
5. B. Baking soda is sodium hydrogencarbonate (NaHCO₃), also called sodium bicarbonate. Washing soda is sodium carbonate, option A, which is a different compound.

How to prepare acids, bases and metals

Use pairs. Memorise "acid with its source" and "compound with its common name" as two-column tables. Many questions are "which pair is correct/incorrect" and the odd-pair question in this set (question 2) is a typical form.

For metals, a one-page reactivity series (potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, silver, gold) lets you answer displacement and extraction questions. Learn the alloys as well: brass (copper and zinc), bronze (copper and tin), steel (iron with carbon) and solder (tin and lead).

For everyday compounds, memorise four groups: baking soda (NaHCO₃), washing soda (Na₂CO₃), bleaching powder (calcium oxychloride, used for disinfecting water) and plaster of Paris (calcium sulphate hemihydrate). Know one use for each.

Do not try to master balancing equations or electrochemistry for this exam. TNPSC's science questions test recognition, not calculation. For the first chemistry block, see TNPSC chemistry: atoms and elements practice.

Take the full topic test on PrepMatic

PrepMatic topic tests are about 15 questions in 30 minutes, which makes them a convenient end-of-week check on science. If you are balancing study with work, the study plan has light, moderate and intense paces and lets you choose the days you study. Your reminders can go by browser notification or email.

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