Chapter 2 · CBSE Board 2027

Acids, Bases and Salts Class 10 important questions with answers

The 10 questions to practise first, picked from every CBSE board paper 2023–2026. Each one has the official answer and how to write it for full marks. Then try the free 10-question test.

Chemical Substances – Nature and Behaviour unit: 7 of 80 marks 186 board questions on this chapter since 2023

What comes in the exam

  • Acids, Bases and Salts is part of the Chemical Substances unit, which is worth 25 marks in all.
  • About half the questions are 1-mark MCQs, then 3-mark and 2-mark questions, with a few 4-mark case studies, 5-mark questions and Assertion–Reason.
  • Almost every year you get questions on the pH scale and pH in daily life, indicators, how acids react with metals and carbonates, and why acids conduct only in water.
  • Salts come almost every year too: the chlor-alkali process, baking soda, washing soda, Plaster of Paris and water of crystallisation, often as 3-mark 'name, formula, equation, uses' questions.

Top 10 Acids, Bases and Salts questions from board papers

Real CBSE questions, printed as they appeared. Open each answer to see the marking and the steps.

  1. Q1 Short answer · 3 marks CBSE · 2026

    Ant sting acid; two reasons

    (a) Name the acid present in ant's sting. (b) Give reason : (i) While diluting an acid, it is recommended that the acid should be added to water. (ii) Baking soda is used as an antacid.

    Answer and marking
    1. (a) Name the acid in an ant's sting and give its formula. Methanoic acid (formic acid), HCOOH 1 mark
    2. (b)(i) Mixing acid with water gives out a lot of heat. Adding acid to water avoids excessive local heating, splashing and burns 1 mark
    3. (ii) Link baking soda's nature to the extra acid in the stomach. Baking soda is alkaline and neutralises excess acid in the stomach, giving relief 1 mark

    Answer: (a) Methanoic (formic) acid ; (b)(i) avoids heating, splashing, burns ; (ii) alkaline, neutralises excess stomach acid

    Marks: Acid 1 · Reason (i) 1 · Reason (ii) 1

    For full marks: In (b)(ii) use the word 'neutralises' with 'excess acid in the stomach'.

    Where students lose marks: Writing 'acetic acid' for the ant sting; that is the acid in vinegar.

    CBSE marking scheme

    (a) Methanoic acid / formic acid, HCOOH (1). (b)(i) Adding acid to water avoids excessive local heating, splashing and burns (1). (ii) Baking soda is alkaline and neutralises excess acid in the stomach, giving relief (1).

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  2. Q2 Short answer · 3 marks CBSE · 2026

    Explain the chlor-alkali process

    Explain chlor-alkali process with chemical equation. Name the products formed at anode and cathode.

    Answer and marking
    1. Say what electricity does to brine and why the name fits. Electricity passed through brine decomposes it to sodium hydroxide (alkali) and chlorine, hence chlor-alkali 1 mark
    2. Write the balanced equation with state symbols. 2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g) 1 mark
    3. Name the product at the anode. Anode: Cl₂ (chlorine gas) 0.5 marks
    4. Name the product at the cathode. Cathode: H₂ (hydrogen gas) 0.5 marks

    Answer: Brine electrolysed: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ ; anode Cl₂, cathode H₂

    Marks: Explanation 1 · Equation 1 · Anode ½ · Cathode ½

    For full marks: Explain the name: 'chlor' for chlorine and 'alkali' for sodium hydroxide.

    Where students lose marks: Swapping the electrodes — chlorine forms at the anode, hydrogen at the cathode.

    CBSE marking scheme

    Electricity passed through brine decomposes it to sodium hydroxide (alkali) and chlorine, hence chlor-alkali (1); 2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g) (1); anode: Cl2 (½); cathode: H2 (½).

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  3. Q3 Short answer · 3 marks CBSE · 2026

    Ant sting relief; pH 3.0 and 9.5

    (A) Name the acid present in ant sting and give its chemical formula. Give the common method to get relief from the pain and irritation caused by ant sting. (B) Two solutions 'X' and 'Y' have pH values 3.0 and 9.5 respectively. Which of these will turn blue litmus to red and which will turn phenolphthalein from colourless to pink?

    Answer and marking
    1. (A) Name the acid in an ant's sting. Methanoic (formic) acid 0.5 marks
    2. Give its formula. HCOOH 0.5 marks
    3. A mild base neutralises the acid, so suggest one. Rub a mild base like baking soda on the stung area 1 mark
    4. (B) pH below 7 is acidic, and acids turn blue litmus red. X (pH 3, acidic) turns blue litmus red 0.5 marks
    5. pH above 7 is basic, and bases turn phenolphthalein pink. Y (pH 9.5, basic) turns phenolphthalein pink 0.5 marks

    Answer: (A) Methanoic acid, HCOOH ; rub baking soda ; (B) X turns blue litmus red, Y turns phenolphthalein pink

    Marks: Acid name and formula 1 · Remedy 1 · X and Y 1

    For full marks: In the remedy say 'mild base like baking soda' — naming a base is what the mark checks.

    Where students lose marks: Swapping X and Y: pH 3 is the acid that turns blue litmus red.

    CBSE marking scheme

    (A) Methanoic (formic) acid (½), HCOOH (½); rub a mild base like baking soda on the area (1). (B) X (pH 3, acidic) turns blue litmus red (½); Y (pH 9.5, basic) turns phenolphthalein pink (½). Reason optional.

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  4. Q4 Short answer · 3 marks CBSE · 2026

    Reasons: dilute, dry HCl, CuSO₄

    Give reasons: (i) For dilution of an acid, acid is added into water and not water into acid. (ii) Dry HCl gas does not turn blue litmus red whereas dilute hydrochloric acid does. (iii) Blue colour of Copper(II) sulphate crystals turns white on heating.

    Answer and marking
    1. (i) Diluting acid gives out a lot of heat; say why the order matters. Adding acid to water avoids excessive local heating; adding water to acid may make the mixture splash out and cause burns 1 mark
    2. (ii) Acidic behaviour needs H⁺ ions, which form only in water. Dry HCl does not ionise to give H⁺ ions; in dilute HCl, H⁺ ions are present 1 mark
    3. (iii) The blue colour comes from the water in the crystals. The crystals lose their 5 molecules of water of crystallisation 1 mark

    Answer: (i) Avoids local heating and splashing ; (ii) dry HCl gives no H⁺ ions ; (iii) water of crystallisation is lost

    Marks: Reason (i) 1 · Reason (ii) 1 · Reason (iii) 1

    For full marks: In (ii) write 'H⁺ ions' — the reason is about ions forming only in water.

    Where students lose marks: In (iii) saying the copper sulphate burns or decomposes; it only loses its water of crystallisation.

    CBSE marking scheme

    (i) Adding acid to water avoids excessive local heating; adding water to acid may make the mixture splash out and cause burns (1). (ii) Dry HCl does not ionise to give H+ ions; in dilute HCl H+ ions are present (1). (iii) The crystals lose their 5 molecules of water of crystallisation (1).

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  5. Q5 Case study · 4 marks CBSE · 2026

    Case: pH in daily life

    The pH plays an important role in our daily life. Strength of acids and bases depends on the number of H+ ions and OH– ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution. Answer the following: (i) What type of indicator is used to predict how strong an acid or base is? (ii) Three solutions A, B and C showed pH as 3, 5 and 7. Which solution has the highest concentration of H+ ions? (iii) What are strong acids and weak acids? OR (iii) (1) Under what condition is rainwater called acid rain? (2) In the following acids, identify weak acids: Nitric acid, hydrochloric acid, acetic acid, sulphuric acid, formic acid.

    Answer and marking
    1. (i) Name the indicator that shows different colours across the pH range. Universal indicator 1 mark
    2. (ii) Lower pH means more H⁺ ions; pick the lowest. A (pH 3) 1 mark
    3. (iii) Define strong acids by how many H⁺ ions they give. Strong acids give more H⁺ ions in water (pH about 1–2) 1 mark
    4. Define weak acids the same way. Weak acids give fewer H⁺ ions in water (so a higher pH than a strong acid of the same concentration, but still below 7) 1 mark
    5. (iii) OR (1) Normal rain is slightly acidic; acid rain is below a set pH. Rainwater is acid rain when its pH is less than 5.6 1 mark
    6. (2) Mineral acids are strong; acids from living things here are weak. Weak acids: acetic acid, formic acid 1 mark

    Answer: (i) Universal indicator ; (ii) A ; (iii) (a) strong acids give more H⁺ ions, weak acids fewer / (b) pH below 5.6; acetic and formic acid

    Marks: Indicator 1 · Solution A 1 · Part (iii) 2

    For full marks: Define both terms using 'H⁺ ions' — each definition earns 1 mark.

    Where students lose marks: Picking C (pH 7) as having most H⁺ ions; a higher pH means fewer H⁺ ions.

    CBSE marking scheme

    (i) Universal indicator (1). (ii) A (pH 3) (1). (iii) Strong acids give more H+ ions in water (pH ~1–2); weak acids give fewer H+ ions (pH ~6–7) (1+1). OR (iii) (1) when its pH is less than 5.6 (1); (2) weak acids: acetic acid, formic acid (1).

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  1. Q6 Case study · 4 marks CBSE · 2025

    Case: common salt, raw material

    Common salt is a very important chemical compound for our daily life. Its chemical name is sodium chloride and it is used as a raw material in the manufacture of caustic soda, washing soda, baking soda etc. It is also used in the preservation of pickles, butter, meat etc. (i) Name the acid and the base from which common salt can be obtained. (1) (ii) State the nature (acidic/basic/neutral) of sodium chloride. Give reason for your answer. (1) (iii) (A) What happens when electric current is passed through an aqueous solution of sodium chloride (called brine)? Name the products obtained along with the corresponding places in the electrolytic cell where each of these products is obtained. (2) OR (iii) (B) How is washing soda obtained from sodium chloride? Give chemical equations of the reactions involved in the process. (2)

    Answer and marking
    1. (i) Sodium comes from the base, chloride from the acid. Hydrochloric acid (HCl) and sodium hydroxide (NaOH) 1 mark
    2. (ii) State its nature. Neutral 0.5 marks
    3. Give the reason from the acid and base strengths. It is a salt of a strong acid and a strong base 0.5 marks
    4. (iii)(A) Electric current breaks brine down. Brine decomposes 0.5 marks
    5. Name where the alkali collects. NaOH solution forms near the cathode 0.5 marks
    6. Name the gas at the positive electrode. Cl₂ at the anode 0.5 marks
    7. Name the gas at the negative electrode. H₂ at the cathode 0.5 marks
    8. (iii)(B) First make baking soda from brine, CO₂ and NH₃. NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃ 0.5 marks
    9. Heat the baking soda to get sodium carbonate. 2NaHCO₃ →(heat) Na₂CO₃ + H₂O + CO₂ 0.5 marks
    10. Recrystallise sodium carbonate with water to get washing soda. Recrystallisation: Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O 1 mark

    Answer: (i) HCl and NaOH ; (ii) neutral, strong acid + strong base ; (iii) (A) NaOH near cathode, Cl₂ at anode, H₂ at cathode / (B) NaHCO₃, heat to Na₂CO₃, recrystallise to Na₂CO₃·10H₂O

    Marks: Acid and base 1 · Nature with reason 1 · Part (iii) 2

    For full marks: In (A) name the place of every product — anode or cathode — each one earns ½.

    Where students lose marks: In (B) stopping at Na₂CO₃ and missing the recrystallisation step with 10H₂O.

    CBSE marking scheme

    (i) Hydrochloric acid HCl and sodium hydroxide NaOH (½+½). (ii) Neutral (½) - salt of a strong acid and a strong base (½). (iii)(A) Brine decomposes (½): NaOH solution near the cathode, Cl2 at the anode, H2 at the cathode (½ × 3). OR (B) NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3; 2NaHCO3 →(heat) Na2CO3 + H2O + CO2; recrystallisation: Na2CO3 + 10H2O → Na2CO3.10H2O (½ × 4).

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  2. Q7 Case study · 4 marks CBSE · 2025

    Case: seawater and rock salt

    Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use. (a) Write balanced chemical equation to show the products formed during electrolysis of brine. (1) (b) List two uses of any one product obtained during electrolysis of brine. (1) (c) (i) A mild non-corrosive basic salt 'A', used for faster cooking, is strongly heated to produce a compound 'B', that is used for removing permanent hardness of water. Identify A and B and also write the equation for the reaction that occurs when A is heated. (2) OR (c) (ii) Define water of crystallisation. Give two examples of salts that have water of crystallisation. (2)

    Answer and marking
    1. (a) Write the balanced equation with electricity over the arrow. 2NaCl + 2H₂O →(electricity) 2NaOH + H₂ + Cl₂ 1 mark
    2. (b) Pick one product and give two of its uses. NaOH: soaps and detergents ; paper making 1 mark
    3. (c)(i) The mild basic salt used for faster cooking is A. A = NaHCO₃ (baking soda) 0.5 marks
    4. Heating it gives the salt that removes permanent hardness. B = Na₂CO₃ (sodium carbonate) 0.5 marks
    5. Write the balanced equation for heating A. 2NaHCO₃ →(heat) Na₂CO₃ + H₂O + CO₂ 1 mark
    6. (c)(ii) Define it using 'fixed number' and 'formula unit'. Water of crystallisation: fixed number of water molecules present in one formula unit of a salt 1 mark
    7. Give two hydrated salts with their formulae. CuSO₄·5H₂O ; Na₂CO₃·10H₂O 1 mark

    Answer: (a) 2NaCl + 2H₂O → 2NaOH + H₂ + Cl₂ ; (b) two uses of one product ; (c) (i) A = NaHCO₃, B = Na₂CO₃, 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ / (ii) fixed water molecules per formula unit; CuSO₄·5H₂O, Na₂CO₃·10H₂O

    Marks: Equation 1 · Two uses 1 · Part (c) 2

    For full marks: In (b) give both uses for the SAME product — the question asks for one product only.

    Where students lose marks: In (b) mixing uses of two different products, e.g. one for NaOH and one for chlorine.

    CBSE marking scheme

    (a) 2NaCl + 2H2O —electricity→ 2NaOH + H2 + Cl2 (1). (b) Any two uses of one product — NaOH: degreasing metals, soaps/detergents, paper, artificial fibres; H2: fuel, margarine, ammonia; Cl2: water treatment, PVC, disinfectant, bleach (½+½). (c)(i) A = NaHCO3 baking soda (½), B = Na2CO3 sodium carbonate (½); 2NaHCO3 —heat→ Na2CO3 + H2O + CO2 (1). OR (c)(ii) Fixed number of water molecules present in one formula unit of a salt (1); any two: CuSO4·5H2O, Na2CO3·10H2O, CaSO4·2H2O, FeSO4·7H2O (½+½).

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  3. Q8 Case study · 4 marks CBSE · 2024

    Case: salts in daily life

    Salts play a very important role in our daily life. Sodium chloride which is known as common salt is used almost in every kitchen. Baking soda is also a salt used in faster cooking as well as in baking industry. The family of salts is classified on the basis of cations and anions present in them. (i) Identify the acid and base from which sodium chloride is formed. (1) (ii) Find the cation and the anion present in calcium sulphate. (1) (iii) "Sodium chloride and washing soda both belong to the same family of salts." Justify this statement. (2) OR (iii) Define the term pH scale. Name the salt obtained by the reaction of potassium hydroxide and sulphuric acid and give the pH value of its aqueous solution. (2)

    Answer and marking
    1. (i) Sodium comes from the base, chloride from the acid; name the acid. Acid: HCl 0.5 marks
    2. Now name the base. Base: NaOH 0.5 marks
    3. (ii) Split CaSO₄ into its positive ion first. Cation: Ca²⁺ 0.5 marks
    4. Then its negative ion, with charge. Anion: SO₄²⁻ 0.5 marks
    5. (iii) First state the rule for what makes salts one family. Salts with the same cation (or anion) belong to one family 1 mark
    6. Now find the ion that both salts share. NaCl and washing soda (Na₂CO₃) both have Na⁺, so they belong to the sodium family 1 mark
    7. (iii) OR: say what the pH scale measures. pH scale measures hydrogen ion concentration in a solution 1 mark
    8. KOH and H₂SO₄ make a potassium salt; name it. Potassium sulphate, K₂SO₄ 0.5 marks
    9. A strong acid and strong base give a neutral salt. pH = 7 0.5 marks

    Answer: (i) HCl and NaOH ; (ii) Ca²⁺, SO₄²⁻ ; (iii) (a) both contain Na⁺ — sodium family / (b) pH scale measures H⁺ concentration; K₂SO₄, pH 7

    Marks: Acid and base 1 · Ions 1 · Part (iii) 2

    For full marks: In (iii) name the common ion, 'both contain Na⁺' — that is what makes them one family.

    Where students lose marks: Writing the anion as SO₄ without the 2− charge, which loses the ½.

    CBSE marking scheme

    (i) HCl and NaOH (½, ½). (ii) Cation Ca2+, anion SO4 2− (½, ½). (iii) Salts with the same cation (or anion) form a family; NaCl and washing soda Na2CO3 both have Na+, so they belong to the sodium family (2). OR (iii) pH scale measures hydrogen ion concentration in a solution (1); potassium sulphate K2SO4 (½); pH = 7 (½).

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  4. Q9 Long answer · 5 marks CBSE · 2024

    Order five solutions by pH

    (i) Five solutions A, B, C, D and E when tested with pH paper showed pH as 4, 1, 13, 7 and 10 respectively. Which solution is: (1) Strongly acidic (2) Strongly alkaline (3) Weakly acidic (4) Neutral and (5) Weakly alkaline? Arrange the solutions in increasing order of H+ ion concentration. (ii) Write the name and formula of (1) an acidic salt and (2) a basic salt giving the name of the parent acid and parent base used to form the salt in each case.

    Answer and marking
    1. (i) Below 7 is acidic, above 7 basic; the farther from 7, the stronger. Strongly acidic: B (pH 1) ; Strongly alkaline: C (pH 13) ; Weakly acidic: A (pH 4) ; Neutral: D (pH 7) ; Weakly alkaline: E (pH 10) 2.5 marks
    2. Lower pH means more H⁺ ions, so list from highest pH to lowest. Increasing [H⁺]: C < E < D < A < B 0.5 marks
    3. (ii) A strong acid with a weak base gives an acidic salt. Acidic salt: ammonium chloride, NH₄Cl 0.5 marks
    4. Name the acid and base it comes from. Parent acid: HCl ; parent base: NH₄OH 0.5 marks
    5. A weak acid with a strong base gives a basic salt. Basic salt: sodium carbonate, Na₂CO₃ 0.5 marks
    6. Name the acid and base it comes from. Parent acid: H₂CO₃ ; parent base: NaOH 0.5 marks

    Answer: (i) B, C, A, D, E; C < E < D < A < B (ii) NH₄Cl (HCl + NH₄OH); Na₂CO₃ (H₂CO₃ + NaOH)

    Marks: Five identifications 2½ · [H⁺] order ½ · Two salts 1 · Parent acids and bases 1

    For full marks: Each salt earns two halves: one for name and formula, one for its parent acid AND base.

    Where students lose marks: Writing the [H⁺] order by pH (B < A < D < E < C): more H⁺ means LOWER pH, so the order reverses.

    CBSE marking scheme

    (i) Strongly acidic B; strongly alkaline C; weakly acidic A; neutral D; weakly alkaline E (½×5). Increasing [H+]: C < E < D < A < B (½). (ii) Acidic salt: ammonium chloride NH4Cl (½), from HCl and NH4OH (½). Basic salt: sodium carbonate Na2CO3 (½), from H2CO3 and NaOH (½). (Any other correct salts.)

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  5. Q10 Long answer · 5 marks CBSE · 2023

    Reverse litmus change; bases

    (i) An aqueous solution turns blue litmus red. Which of the following solutions when added in excess would reverse the change ? (1) Lemon juice (2) Magnesium hydroxide (3) Vinegar (4) Calcium sulphate (ii) Out of the following, which compound/compounds will turn the phenolphthalein solution pink ? (1) CH3COOH (2) Ca(OH)2 (3) HCl (4) NaOH (iii) Name a gas whose aqueous solution is basic. Write the formula/name of this solution. (iv) A basic substance is used to treat a honey-bee sting. Why ? (v) Name the acid which is present in (1) Tomato and (2) Tamarind.

    Answer and marking
    1. (i) The solution is acidic, so an excess of base turns red litmus back blue. (2) Magnesium hydroxide 1 mark
    2. (ii) Phenolphthalein turns pink only in a base; pick the bases. Ca(OH)₂ 0.5 marks
    3. The second base in the list also turns it pink. NaOH 0.5 marks
    4. (iii) Name the gas that dissolves in water to give a base. Ammonia gas, NH₃ 0.5 marks
    5. Then name the basic solution it forms. Ammonium hydroxide, NH₄OH 0.5 marks
    6. (iv) The sting puts an acid into the skin; a base cancels it. The base neutralises the methanoic acid of the bee sting. 1 mark
    7. (v) Recall the natural acid in each food. Tomato: oxalic acid 0.5 marks
    8. Tamarind has a different acid. Tamarind: tartaric acid 0.5 marks

    Answer: (i) (2) Mg(OH)₂ (ii) Ca(OH)₂ and NaOH (iii) NH₃, NH₄OH (iv) neutralises methanoic acid (v) oxalic; tartaric

    Marks: (i) 1 · (ii) 1 · (iii) 1 · (iv) and (v) 2

    For full marks: In (ii) write BOTH Ca(OH)₂ and NaOH — each base is a separate ½.

    Where students lose marks: Choosing calcium sulphate in (i): it is a salt, not a base, so it cannot reverse the acid's change.

    CBSE marking scheme

    (i) (2) Magnesium hydroxide (1). (ii) Ca(OH)2 and NaOH (½ + ½). (iii) Ammonia, NH3 (½); NH4OH, ammonium hydroxide (½). (iv) To neutralise the acid (methanoic acid) of the bee sting (1). (v) Tomato: oxalic acid; tamarind: tartaric acid (½ + ½).

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Free 10-question test: Acids, Bases and Salts

MCQ and Assertion–Reason questions from CBSE papers. About 10 minutes. Your score shows straight away.

  1. MCQ · CBSE · 2026

    During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through a guard tube containing calcium chloride. The role of CaCl2 taken in guard tube is to –

  2. MCQ · CBSE · 2026

    Which of the following acid-base indicators will be used by a visually challenged student to detect the presence of acid in a given solution?

  3. MCQ · CBSE · 2026

    When zinc reacts with NaOH, the product formed is:

  4. MCQ · CBSE · 2026

    The natural sources of oxalic acid, lactic acid and methanoic acid respectively are:

  5. Assertion–Reason · CBSE · 2026

    Assertion (A): Sodium acetate is a basic salt. Reason (R): It is because it is a salt of weak acid and strong base.

  6. MCQ · CBSE · 2026

    To a small amount of copper oxide in a beaker, when we add dilute hydrochloric acid slowly with stirring, the change in the colour of the solution is due to the formation of:

  7. MCQ · CBSE · 2026

    Which one of the following can be used as an acid-base indicator by a visually impaired (blind) student?

  8. MCQ · CBSE · 2026

    An aqueous solution turns red litmus blue. Excess addition of which of the following solution would reverse the change?

  9. MCQ · CBSE · 2026

    A metal carbonate reacts with a solution X which forms a salt, water and a gas Y. What are X and Y?

  10. MCQ · CBSE · 2025

    Which of the given option represents a family of salts?

Common mistakes in Acids, Bases and Salts

Mistake Leaving a preparation equation unbalanced.

Fix Count every atom on both sides before you move on. For brine, check Na, Cl, H and O. The scheme cuts ½ mark for an equation that is not balanced.

Mistake Mixing up gypsum and Plaster of Paris.

Fix They differ only in their water of crystallisation. Write the right number of water molecules in each formula, and write 373 K over the arrow when gypsum is heated. Give the chemical name and the formula: each carries ½ mark.

Mistake Writing 'acid is added to water' with no reason.

Fix Give the reason: mixing gives out a lot of heat. If water is added to acid, the mixture can boil and splash out and cause burns. So the acid is added slowly to water, with constant stirring. Do this only in the school lab, with your teacher. In Assertion–Reason, read which way round the assertion says it.

Mistake Not knowing which bleaching powder formula to write.

Fix Write CaOCl₂, made from slaked lime and dry chlorine: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. The book's form also earns the mark: Ca(ClO)₂, from 2Ca(OH)₂ + 2Cl₂ → Ca(ClO)₂ + CaCl₂ + 2H₂O.

Mistake Mixing up what each indicator does in acid and in base.

Fix First decide from the pH: below 7 is acidic, above 7 is basic. Acids turn blue litmus red; bases turn red litmus blue. Phenolphthalein is colourless in acid and pink in base. The lower the pH, the more H⁺ ions.

Mistake Calling every salt neutral.

Fix Look at the acid and the base the salt comes from. Strong acid + strong base gives a neutral salt. Weak acid + strong base gives a basic salt, like Na₂CO₃. Strong acid + weak base gives an acidic salt. Write the parent acid and base as your reason.

How to write for full marks

  • For a salt question, answer every part asked: chemical name, formula, preparation equation and uses. Often the name, the formula and each use carry ½ mark each.
  • Write the condition over the arrow: electricity for brine, heat when baking soda turns into sodium carbonate, 373 K for gypsum. Add state symbols like (aq) and (g) to the chlor-alkali equation.
  • For electrolysis of brine, name what forms at the anode, at the cathode and near the cathode separately. Each product carries its own ½ mark.
  • For 'give reason' about acids and bases, link your answer to H⁺ or OH⁻ ions in water. Each reason carries 1 mark, so write one full sentence for each.
  • To design the 'acids conduct' set-up, draw or describe the beaker, two electrodes, bulb, battery and switch, then say what you see with each solution. The scheme also gives the marks when it is explained in words.

Not in the 2026-27 exam

Leave these out of your revision.

  • Defining pH using logarithms
  • Information in the NCERT boxes

Questions students ask

Which Acids, Bases and Salts questions are most important for the Class 10 board exam 2027?

Expect MCQs on pH, indicators and salt types, and 3-mark questions on the formula, preparation equation and uses of baking soda, washing soda, bleaching powder or Plaster of Paris. The 10 questions on this page are real CBSE board questions from 2023–2026, chosen across the chapter's topics and question types.

How many marks does Acids, Bases and Salts carry in the Class 10 board exam?

Acids, Bases and Salts is part of the Chemical Substances – Nature and Behaviour unit, which carries 7 of the 80 theory marks in the CBSE Class 10 Science paper.

Are these real CBSE previous year questions?

Yes. Each question is printed as it appeared in a CBSE board paper or sample paper, with its source, and the answer follows CBSE's official marking scheme.

All Class 10 Science chapters

Questions and answers: CBSE board papers, sample papers and official marking schemes, 2023–2026. Worked steps and tips: Dhee.