NCERT Exemplar Solutions for Class 10 Science Chapter 2 provide detailed explanations and answers to the exercises in the chapter “Acids, Bases, and Salts.” These solutions help students understand the key concepts, solve complex problems, and prepare effectively for exams by offering step-by-step guidance and practice questions aligned with the NCERT curriculum.
Multiple Choice Questions
- What happens when a solution of an acid is mixed with a solution
of a base in a test tube?
(i) The temperature of the solution increases
(ii) The temperature of the solution decreases
(iii) The temperature of the solution remains the same
(iv) Salt formation takes place
(a) (i) only (b) (i) and (iii)
(c) (ii) and (iii) (d) (i) and (iv)
ANSWER – (d) (i) and (iv)
REASON – When a solution of an acid is mixed with a solution of a base in a test tube, a neutralization reaction occurs. During this reaction: (i) The temperature of the solution increases because the reaction is exothermic, releasing heat. (iv) Salt formation takes place as the acid and base react to form water and a salt.
2. An aqueous solution turns red litmus solution blue. Excess
addition of which of the following solution would reverse the
change?
(a) Baking powder
(b) Lime
(c) Ammonium hydroxide solution
(d) Hydrochloric acid
ANSWER – (d) Hydrochloric acid
REASON – An aqueous solution that turns red litmus solution blue indicates that the solution is basic. To reverse this change, an acid needs to be added to neutralize the basic solution.
3. During the preparation of hydrogen chloride gas on a humid day,
the gas is usually passed through the guard tube containing calcium
chloride. The role of calcium chloride taken in the guard tube is to
(a) absorb the evolved gas
(b) moisten the gas
(c) absorb moisture from the gas
(d) absorb Cl– ions from the evolved gas
ANSWER – (c) absorb moisture from the gas.
REASON – Calcium chloride is a hygroscopic substance, meaning it has a strong affinity for water and readily absorbs moisture from the gas, ensuring that the hydrogen chloride gas produced remains dry.
4. Which of the following salts does not contain water of crystallisation?
(a) Blue vitriol
(b) Baking soda
(c) Washing soda
(d) Gypsum
ANSWER – (b) Baking soda
REASON – Baking soda, chemically known as sodium bicarbonate (NaHCO3), is anhydrous, meaning it does not contain water of crystallization.
5. Sodium carbonate is a basic salt because it is a salt of
(a) strong acid and strong base
(b) weak acid and weak base
(c) strong acid and weak base
(d) weak acid and strong base
ANSWER – (d) weak acid and strong base.
REASON – The weak acid in this case is carbonic acid (H₂CO₃), and the strong base is sodium hydroxide (NaOH). The reaction between these two forms sodium carbonate and water, resulting in a basic salt.
6.Calcium phosphate is present in tooth enamel. Its nature is
(a) basic
(b) acidic
(c) neutral
(d) amphoteric
ANSWER – (a) basic.
REASON – Calcium phosphate can react with acids (such as those produced by bacteria in the mouth) to help neutralize them, thereby protecting tooth enamel. This basic nature helps in maintaining the pH balance in the mouth.
7. A sample of soil is mixed with water and allowed to settle. The
clear supernatant solution turns the pH paper yellowish-orange.
Which of the following would change the colour of this pH paper
to greenish-blue?
(a) Lemon juice
(b) Vinegar
(c) Common salt
(d) An antacid
ANSWER – (d) An antacid.
REASON – Antacids are basic substances that neutralize acids, thus raising the pH of the solution and changing the pH paper to a greenish-blue color.
8. Which of the following gives the correct increasing order of acidic
strength?
(a) Water <Acetic acid <Hydrochloric acid
(b) Water <Hydrochloric acid <Acetic acid
(c) Acetic acid <Water <Hydrochloric acid
(d) Hydrochloric acid <Water <Acetic acid
ANSWER – (a) Water < Acetic acid < Hydrochloric acid
REASON – Water is neutral or very weakly acidic, acetic acid is a weak acid, and hydrochloric acid is a strong acid. Therefore, the order from weakest to strongest acid is water, then acetic acid, and finally hydrochloric acid.
9.If a few drops of a concentrated acid accidentally spills over the
hand of a student, what should be done?
(a) Wash the hand with saline solution
(b) Wash the hand immediately with plenty of water and apply a
paste of sodium hydrogencarbonate
(c) After washing with plenty of water apply solution of sodium
hydroxide on the hand
(d) Neutralise the acid with a strong alkali
ANSWER – (b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogencarbonate.
REASON –Washing with plenty of water helps to dilute and remove the acid. Applying a paste of sodium hydrogencarbonate (baking soda) will help to neutralize any remaining acid on the skin.
10.Sodium hydrogencarbonate when added to acetic acid evolves a gas.
Which of the following statements are true about the gas evolved?
(i) It turns lime water milky
(ii) It extinguishes a burning splinter
(iii) It dissolves in a solution of sodium hydroxide
(iv) It has a pungent odour
(a) (i) and (ii) (b) (i), (ii) and (iii)
(c) (ii), (iii) and (iv) (d) (i) and (iv)
ANSWER – (b) (i), (ii) and (iii).
REASON – When sodium hydrogencarbonate (baking soda) is added to acetic acid, the gas evolved is carbon dioxide (CO₂). The properties of carbon dioxide relevant to the statements provided are:
(i) It turns lime water milky. (ii) It extinguishes a burning splinter. (iii) It dissolves in a solution of sodium hydroxide. (iv) It has a pungent odour.
11.Common salt besides being used in kitchen can also be used as
the raw material for making
(i) washing soda
(ii) bleaching powder
(iii) baking soda
(iv) slaked lime
(a) (i) and (ii) (b) (i), (ii) and (iv)
(c) (i) and (iii) (d) (i), (iii) and (iv)
ANSWER – (c) (i) and (iii)
REASON – Common salt (sodium chloride, NaCl) is used as a raw material for making:
(i) Washing soda (sodium carbonate, Na₂CO₃) (ii) Bleaching powder (calcium hypochlorite, Ca(OCl)₂) (iii) Baking soda (sodium bicarbonate, NaHCO₃)
It is not used to make slaked lime (calcium hydroxide, Ca(OH)₂).
12.
One of the constituents of baking powder is sodium
hydrogencarbonate, the other constituent is
(a) hydrochloric acid
(b) tartaric acid
(c) acetic acid
(d) sulphuric acid
ANSWER – (b) tartaric acid
REASON – Baking powder typically contains a mixture of an acid (such as tartaric acid) and a base (such as sodium hydrogencarbonate, also known as baking soda). When mixed with water, these ingredients react to produce carbon dioxide gas, which helps baked goods rise.
To protect tooth decay we are advised to brush our teeth regularly.
The nature of the tooth paste commonly used is
(a) acidic
(b) neutral
(c) basic
(d) corrosive
ANSWER – (c) basic
REASON – Toothpaste generally has a basic (alkaline) nature to help neutralize the acids produced by bacteria in the mouth, which can contribute to tooth decay.
Which of the following statements is correct about an aqueous
solution of an acid and of a base?
(i) Higher the pH, stronger the acid
(ii) Higher the pH, weaker the acid
(iii) Lower the pH, stronger the base
(iv) Lower the pH, weaker the base
(a) (i) and (iii) (b) (ii) and (iii)
(c) (i) and (iv) (d) (ii) and (iv)
ANSWER – (d) (ii) and (iv)
REASON –
The correct statements about an aqueous solution of an acid and of a base are:
(ii) Higher the pH, weaker the acid (iv) Lower the pH, weaker the base
The pH of the gastric juices released during digestion is
(a) less than 7
(b) more than 7
(c) equal to 7
(d) equal to 0
ANSWER – (a) less than 7
REASON – Gastric juices are highly acidic, typically having a pH around 1.5 to 3.5, which helps in the digestion of food and killing harmful bacteria.
Which of the following phenomena occur, when a small amount of
acid is added to water?
(i) Ionisation
(ii) Neutralisation
(iii) Dilution
(iv) Salt formation
(a) (i) and (ii) (b) (i) and (iii)
(c) (ii) and (iii) (d) (ii) and (iv)
ANSWER – (b) (i) and (iii).
REASON –
When a small amount of acid is added to water, the following phenomena occur:
(i) Ionisation (iii) Dilution
Which one of the following can be used as an acid–base indicator
by a visually impared student?
(a) Litmus
(b) Turmeric
(c) Vanilla essence
(d) Petunia leaves
ANSWER – (c) Vanilla essence
REASON – Vanilla essence can be used as an acid-base indicator by visually impaired students because it undergoes a noticeable change in smell rather than color. In acidic conditions, the smell of vanilla is retained, while in basic conditions, the smell of vanilla is diminished or altered. This allows a visually impaired person to detect the pH change through their sense of smell.
Which of the following substance will not give carbon dioxide on
treatment with dilute acid?
(a) Marble
(b) Limestone
(c) Baking soda
(d) Lime
ANSWER – (d) Lime
REASON – Lime, also known as calcium oxide (CaO), does not produce carbon dioxide when treated with dilute acid. Instead, it forms calcium salts and water. Marble and limestone, both primarily composed of calcium carbonate (CaCO₃), and baking soda (sodium bicarbonate, NaHCO₃) do release carbon dioxide when treated with dilute acids.
Which of the following is acidic in nature?
(a) Lime juice
(b) Human blood
(c) Lime water
(d) Antacid
ANSWER – (a) Lime juice
REASON – Lime juice contains citric acid, which gives it its acidic properties. Human blood is slightly basic, lime water (calcium hydroxide solution) is basic, and antacids are also basic as they are used to neutralize stomach acid.
In an attempt to demonstrate electrical conductivity
through an electrolyte, the following apparatus
(Figure 2.1) was set up.
Which among the following statement(s) is(are)
correct?
(i) Bulb will not glow because electrolyte is not
acidic
(ii) Bulb will glow because NaOH is a strong base
and furnishes ions for conduction.
(iii) Bulb will not glow because circuit is incomplete
(iv) Bulb will not glow because it depends upon
the type of electrolytic solution
(a) (i) and (iii) (b) (ii) and (iv)
(c) (ii) only (c) (iv) only
ANSWER – (c) (ii) only
REASON – The bulb will glow because NaOH is a strong base and dissociates completely in water to furnish a large number of ions, which conduct electricity and complete the circuit.
Which of the following is used for dissolution of gold?
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Nitric acid
(d) Aqua regia
ANSWER – (d) Aqua regia
REASON – Aqua regia is a mixture of hydrochloric acid and nitric acid in a 3:1 ratio, and it is capable of dissolving gold.
Which of the following is not a mineral acid?
(a) Hydrochloric acid
(b) Citric acid
(c) Sulphuric acid
(d) Nitric acid
ANSWER – (b) Citric acid
REASON – Citric acid is an organic acid, not a mineral acid. Hydrochloric acid, sulphuric acid, and nitric acid are all mineral acids.
Which among the following is not a base?
(a) NaOH
(b) KOH
(c) NH4OH
(d) C2H5OH
ANSWER – (d) C2H5OH is not a base.
REASON – It is ethanol, which is an alcohol. Bases are substances that can accept protons (H⁺ ions) or donate hydroxide ions (OH⁻).
Which of the following statements is not correct?
(a) All metal carbonates react with acid to give a salt, water and
carbon dioxide
(b) All metal oxides react with water to give salt and acid
(c) Some metals react with acids to give salt and hydrogen
(d) Some non metal oxides react with water to form an acid
ANSWER – (b) All metal oxides react with water to give salt and acid.
REASON – This statement is not correct. Metal oxides typically react with water to form metal hydroxides, not salts and acids. The correct statement should be that metal oxides react with water to give metal hydroxides and hydrogen gas.
Match the chemical substances given in Column (A) with their
appropriate application given in Column (B)
Column (A) Column (B)
(A) Bleaching powder (i) Preparation of glass
(B) Baking soda (ii) Production of H2
and Cl2
(C) Washing soda (iii) Decolourisation
(D) Sodium chloride (iv) Antacid
(a) A—(ii), B—(i), C—(iv), D—(iii)
(b) A—(iii), B—(ii), C—(iv), D—(i)
(c) A—(iii), B—(iv), C—(i), D—(ii)
(d) A—(ii), B—(iv), C—(i), D—(iii)
ANSWER – The correct matching is: (d) A—(ii), B—(iv), C—(i), D—(iii)
REASON -(A) Bleaching powder is used in the production of H2 and Cl2. (B) Baking soda is not listed. (C) Washing soda is used in the preparation of glass. (D) Sodium chloride is used in decolourisation.