Application Based Questions on - Chapter 1 - Chemical Reactions and Equations -Class 10 CBSE with Answers (MCQ + Case Based + Assertion Reason) - CBSE Class Notes Online

T20 Application-Based and Tricky Questions from Chapter 1: Chemical Reactions and Equations (Class 10 Science). These questions are designed as per the latest CBSE competency-based pattern and focus on real-life applications, daily life examples, redox reactions, balancing of equations, and higher-order thinking skills (HOTS).

Each question is followed by a detailed model answer with proper chemical equations and explanations. A suggested marking scheme is also included to help students understand how to write answers in board exams.

Table of Contents

Application Based tricky Questions

Question 1

A student burns a magnesium ribbon but forgets to clean it with sandpaper first. (a) Predict the difference in observation compared to burning a cleaned ribbon. (b) Explain why cleaning is essential for the chemical reaction to occur properly. (c) Write the balanced chemical equation with physical states.

Model Answer (a) If the magnesium ribbon is not cleaned, it will not burn easily or the flame will not be dazzling white. The ribbon may take longer to catch fire or may burn incompletely with a dull flame.

(b) Magnesium ribbon gets coated with a thin layer of magnesium oxide when exposed to air. This oxide layer prevents the fresh metal from coming in direct contact with oxygen. Cleaning with sandpaper removes this protective oxide layer so that the magnesium can react vigorously with oxygen present in air.

Question 2

Quick lime (calcium oxide) is used in whitewashing. After application on walls, the walls develop a shiny finish after 2–3 days. (a) Write the balanced chemical equations for the two reactions involved. (b) Identify the type of each reaction. (c) Why does the shiny finish appear only after a few days and not immediately?

Model Answer (a) CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

(b) Both reactions are combination reactions. The first reaction is also exothermic because a large amount of heat is released.

(c) The shiny finish appears after 2–3 days because the second reaction (formation of thin layer of calcium carbonate) is slow. It requires carbon dioxide from the atmosphere to react with the slaked lime coated on the wall.

Also Check – Chapter 1 – A Detailed Guide to “Chemical Reactions and Equations” Activities for Class 10 Students

Question 3

In Activity 1.7 (electrolysis of water), the volume of gas collected in one test tube is double that in the other. (a) Identify the two gases and write the balanced chemical equation with states. (b) Why are a few drops of dilute sulphuric acid added to water before electrolysis? (c) Classify the reaction and explain whether it is endothermic or exothermic, giving a reason based on energy change.

Model Answer (a) The gas collected in double volume is hydrogen (at cathode) and the gas in single volume is oxygen (at anode).

Balanced equation: 2H₂O(l) → 2H₂(g) + O₂(g) (with electric current)

(b) Pure water is a poor conductor of electricity. A few drops of dilute sulphuric acid are added to increase the conductivity of water so that electrolysis can take place.

(c) It is a decomposition reaction (specifically electrolytic decomposition). It is endothermic because electrical energy is continuously absorbed to break the bonds in water molecules.

Question 4

When lead nitrate powder is heated strongly in a boiling tube, brown fumes are evolved along with a yellow residue. (a) Write the balanced chemical equation for the reaction. (b) Name the type of reaction and the form of energy supplied. (c) How would you confirm that the brown gas is nitrogen dioxide? Give one industrial or practical context where a similar thermal decomposition is useful.

Model Answer (a) 2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g) (Heat)

(b) It is a thermal decomposition reaction. The energy is supplied in the form of heat.

(c) Bring a glowing splinter near the mouth of the boiling tube — it will rekindle (confirms oxygen). The brown colour and pungent smell confirm nitrogen dioxide. This type of reaction is used in the manufacture of lead oxide and in fireworks.

Question 5

Silver chloride (white) turns grey when exposed to sunlight and is used in black-and-white photography. (a) Write the balanced chemical equation for the change. (b) What type of reaction is this? Name the form of energy that causes the decomposition. (c) Why does silver bromide behave similarly? How does this reaction help in capturing an image on photographic film?

Model Answer (a) 2AgCl(s) → 2Ag(s) + Cl₂(g) (Sunlight)

(b) It is a photochemical decomposition reaction. The energy form involved is light (sunlight).

In black-and-white photography, light reduces silver halide to metallic silver (black/grey), forming the image on the film.

Question 6

An iron nail is left in copper sulphate solution for some time. The blue colour of the solution fades and the nail becomes brownish. (a) Write the balanced chemical equation with state symbols. (b) Identify the type of reaction. Is it also a redox reaction? Justify by naming the substance oxidised and the substance reduced. (c) If a zinc granule is used instead of the iron nail, will the reaction be faster or slower? Explain using reactivity.

Model Answer (a) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

(b) It is a displacement reaction. Yes, it is also a redox reaction. Iron is oxidised and copper ion (Cu²⁺) is reduced.

Question 7

Barium chloride solution is mixed with sodium sulphate solution in a test tube. A white insoluble substance forms immediately. (a) Write the balanced chemical equation with state symbols. (b) Name the white substance and the type of reaction. Why is it specifically called a precipitation reaction? (c) Give one practical application of precipitation reactions in everyday life or laboratory analysis.

Model Answer (a) Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)

(b) The white substance is barium sulphate. It is a double displacement reaction. It is called a precipitation reaction because an insoluble solid (precipitate) is formed.

Question 8

Copper powder is heated in air in a china dish and turns black. Hydrogen gas is then passed over the hot black substance and it turns brown again. (a) Write balanced chemical equations for both steps. (b) In the second reaction, identify the substance that is oxidised and the substance that is reduced. (c) What does this pair of reactions demonstrate about the nature of oxidation and reduction?

Model Answer (a) First: 2Cu(s) + O₂(g) → 2CuO(s) (Heat) Second: CuO(s) + H₂(g) → Cu(s) + H₂O(g) (Heat)

(b) In the second reaction, CuO is reduced and H₂ is oxidised.

Question 9

Respiration in our body is represented by: C₆H₁₂O₆(aq) + 6O₂(aq) → 6CO₂(aq) + 6H₂O(l) + energy

(a) Is this a combination reaction, decomposition reaction, or neither? Justify. (b) Why is respiration considered an exothermic reaction? How does it help maintain body temperature? (c) Is it a redox reaction? Identify the substance oxidised and the substance reduced.

Model Answer (a) It is neither a strict combination nor decomposition reaction because two reactants produce more than one product.

(b) Respiration is exothermic because a large amount of energy is released. This energy helps maintain body temperature and supports body activities.

Question 10

Photosynthesis is represented as: 6CO₂(aq) + 12H₂O(l) → C₆H₁₂O₆(aq) + 6O₂(aq) + 6H₂O(l) (Sunlight + Chlorophyll)

(a) Is this a strict combination reaction (single product)? Explain. (b) Is the reaction endothermic or exothermic? Give reason with reference to the chapter. (c) Is photosynthesis a redox reaction? Briefly justify.

Model Answer (a) No, it is not a strict combination reaction because more than one product is formed.

(b) It is an endothermic reaction because it requires light energy (sunlight) to proceed.

Question 11

When fats and oils in food are left exposed to air for a long time, they become rancid. (a) What type of reaction causes rancidity? (b) Why do chips manufacturers flush the bags with nitrogen gas? (c) How does keeping food in airtight containers help prevent this? Link your answer to a concept from the chapter.

Model Answer (a) Rancidity is caused by oxidation of fats and oils when they react with oxygen present in air.

(b) Nitrogen gas is inert. Flushing chip packets with nitrogen displaces oxygen and creates an inert atmosphere. This prevents the oxidation of fats and oils, keeping the chips fresh for a longer time.

(c) Airtight containers reduce or cut off the contact of food with atmospheric oxygen. Since rancidity is an oxidation reaction, limiting the supply of oxygen slows down the process and prevents food from becoming rancid quickly.

Question 12

Why do we apply paint on iron articles like gates, railings etc.? (a) What chemical process is prevented by painting? (b) Explain how the paint layer protects iron from this process. (c) Besides painting, suggest one more method to prevent this process, based on the chapter concepts.

Model Answer (a) Painting prevents corrosion (rusting) of iron, which is an oxidation reaction.

(b) The paint layer acts as a protective barrier. It prevents direct contact of the iron surface with moisture and oxygen present in the air. Without moisture and oxygen, rusting cannot take place.

Galvanization (coating iron with zinc)
Applying grease or oil
Making alloys (like stainless steel)

Question 13

A student takes about 2 g of barium hydroxide in a test tube and adds 1 g of ammonium chloride and mixes with the help of a glass rod. He touches the bottom of the test tube and feels it cold. (a) Write the possible balanced chemical equation for the reaction. (b) What type of reaction is this? Is it exothermic or endothermic? (c) Explain the temperature change in terms of energy absorbed or released during the reaction.

Model Answer (a) Ba(OH)₂(s) + 2NH₄Cl(s) → BaCl₂(aq) + 2NH₃(g) + 2H₂O(l)

(b) It is a double displacement reaction. It is endothermic (heat is absorbed).

(c) In an endothermic reaction, heat energy is absorbed from the surroundings to break the bonds in the reactants. As a result, the temperature of the reaction mixture falls and the bottom of the test tube feels cold.

Question 14

When zinc granules are added to dilute hydrochloric acid in a conical flask, bubbles of a gas evolve and the flask becomes warm to touch. (a) Write the balanced chemical equation with state symbols. (b) Name the gas evolved and classify the reaction (type + energy change). (c) How can you confirm the identity of the gas? What might happen if the flask is tightly corked?

Model Answer (a) Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

(b) The gas evolved is hydrogen. It is a displacement reaction as well as an exothermic reaction (heat is released).

(c) Bring a burning candle near the mouth of the flask — the gas burns with a pop sound, confirming it is hydrogen. If the flask is tightly corked, pressure will increase and the cork may blow out or the flask may burst.

Question 15

In Activity 1.9, iron nails are dipped in copper sulphate solution while one is kept aside for comparison. (a) Why does the blue colour of copper sulphate solution become lighter in the test tube with nails? (b) Write the balanced equation. How is this reaction different from a double displacement reaction (use the example of barium chloride + sodium sulphate)? (c) Arrange iron, copper, and zinc in order of reactivity based on displacement reactions mentioned in the chapter.

Model Answer (a) The blue colour becomes lighter because copper ions (Cu²⁺) are removed from the solution as they get displaced by iron and deposited as brownish copper metal on the nail.

(b) Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

This is a displacement reaction (a more reactive element displaces a less reactive element). In contrast, barium chloride + sodium sulphate is a double displacement reaction where ions are exchanged between two compounds.

Question 16

Balance the following skeletal equation and identify the type of reaction: Fe + H₂O → Fe₃O₄ + H₂ (when steam is passed over hot iron). Write the fully balanced equation with physical states. Is energy absorbed or released in this reaction?

Model Answer Balanced equation: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)

It is a displacement reaction. In this reaction, heat energy is supplied (iron is heated and steam is passed), so energy is absorbed from outside.

Question 17

A substance ‘X’ is used for whitewashing. It reacts vigorously with water to form substance ‘Y’, releasing a large amount of heat. (a) Identify X and Y. Write the balanced chemical equation for the reaction between X and water. (b) Substance Y further reacts slowly with CO₂ present in air. Write the equation and name the type of reaction. (c) Why is the wall shiny only after 2–3 days?

Model Answer (a) X = Calcium oxide (Quick lime) Y = Calcium hydroxide (Slaked lime)

CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat

(b) Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l) It is a combination reaction.

(c) The wall becomes shiny only after 2–3 days because the reaction of slaked lime with carbon dioxide from air is slow. It takes time for sufficient calcium carbonate to form a thin shining layer.

Question 18

A shiny brown coloured element ‘X’ on heating in air becomes black. When hydrogen gas is passed over this black substance (while heating), it regains its original brown colour. (a) Identify element X and the black compound formed. (b) Write balanced equations for both changes. (c) In the second reaction, which substance is reduced? Justify using the definition of reduction from the chapter.

Model Answer (a) Element X = Copper (Cu) Black compound = Copper(II) oxide (CuO)

(b) First: 2Cu(s) + O₂(g) → 2CuO(s) (Heat) Second: CuO(s) + H₂(g) → Cu(s) + H₂O(g) (Heat)

(c) In the second reaction, CuO is reduced. According to the chapter, reduction is the loss of oxygen. Copper(II) oxide loses oxygen to form copper.

Question 19

Differentiate between a displacement reaction and a double displacement reaction with the help of one example each from the activities described in the chapter. Give one real-life application (other than those in the textbook) for each type of reaction.

Model Answer

Displacement Reaction

A more reactive element displaces a less reactive element from its compound.
Example: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s) (Activity 1.9)
Real-life application: Thermite reaction used to join railway tracks.

Double Displacement Reaction

Exchange of ions takes place between two compounds.
Example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq) (Activity 1.10)
Real-life application: Used in qualitative analysis to test ions and in water softening.

Question 20

“Not every combination reaction is a redox reaction, and not every redox reaction is a combination reaction.” Justify the statement with: (a) One example of a combination reaction that is also a redox reaction (with equation). (b) One example of a combination reaction that is not a redox reaction (with equation). (c) One example of a redox reaction that is not a combination reaction (with equation).

Model Answer

(a) Combination reaction that is also redox: Burning of magnesium 2Mg(s) + O₂(g) → 2MgO(s) (Magnesium gains oxygen → oxidised)

(b) Combination reaction that is not redox: Reaction of quick lime with water CaO(s) + H₂O(l) → Ca(OH)₂(aq) (No substance gains or loses oxygen)

(c) Redox reaction that is not combination: Reaction of iron with copper sulphate Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s) (It is a displacement reaction with multiple products)

Tricky Application-Based MCQs with Answers

Chapter 1: Chemical Reactions and Equations | Class 10 CBSE

Question 1

When a slice of apple is cut and left exposed to air, it turns brown after some time. Which type of reaction is mainly responsible for this change? (a) Combination reaction (b) Decomposition reaction (c) Oxidation reaction (d) Double displacement reaction

Correct Answer: (c) Oxidation reaction Explanation: The browning of apple is due to the oxidation of phenolic compounds present in it when exposed to oxygen in the air.

Question 2

A student added dilute hydrochloric acid to zinc granules taken in a test tube. He observed bubbles of a gas evolving and the test tube becoming warm. Which of the following statements is correct? (a) It is an endothermic displacement reaction (b) It is an exothermic displacement reaction (c) It is a combination reaction (d) No reaction takes place as zinc is less reactive than hydrogen

Correct Answer: (b) It is an exothermic displacement reaction Explanation: Zinc displaces hydrogen from HCl (displacement reaction) and heat is released, making it exothermic.

Question 3

In the refining of silver, silver nitrate solution is treated with copper. Which of the following is correct about this reaction? (a) It is a double displacement reaction (b) Copper is oxidised and silver is reduced (c) Silver is oxidised and copper is reduced (d) It is a photochemical decomposition reaction

Correct Answer: (b) Copper is oxidised and silver is reduced Explanation: Copper displaces silver from silver nitrate. Copper loses electrons (oxidised) and silver ions gain electrons (reduced).

Question 4

Why do manufacturers flush bags of chips with nitrogen gas instead of air? (a) Nitrogen is cheaper than oxygen (b) Nitrogen prevents the oxidation of fats and oils (c) Nitrogen helps in the decomposition of chips (d) Nitrogen increases the taste of chips

Correct Answer: (b) Nitrogen prevents the oxidation of fats and oils Explanation: Nitrogen is an inert gas. It prevents the oxidation (rancidity) of fats and oils present in chips.

Question 5

When iron nails are dipped in copper sulphate solution, the blue colour of the solution fades and the nails become brownish. If zinc granules are used instead of iron nails, the reaction will be: (a) Slower because zinc is less reactive than iron (b) Faster because zinc is more reactive than iron (c) The same because both are metals (d) No reaction will take place

Correct Answer: (b) Faster because zinc is more reactive than iron Explanation: Zinc is more reactive than iron, so it displaces copper from copper sulphate solution at a faster rate.

Question 6

A substance ‘X’ is used for whitewashing. It reacts with water to form ‘Y’ and releases a large amount of heat. ‘Y’ slowly reacts with CO₂ in air to give a shiny finish to the walls. Which of the following is correct? (a) X is Ca(OH)₂ and both reactions are endothermic (b) X is CaO and both reactions are combination reactions (c) X is CaCO₃ and the second reaction is decomposition (d) Both reactions are displacement reactions

Correct Answer: (b) X is CaO and both reactions are combination reactions Explanation: X is quick lime (CaO). Both reactions form a single product, so they are combination reactions.

Question 7

Which of the following reactions is an example of both displacement and redox reaction? (a) CaO + H₂O → Ca(OH)₂ (b) 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃ (c) Fe + CuSO₄ → FeSO₄ + Cu (d) 2AgCl → 2Ag + Cl₂ (Sunlight)

Correct Answer: (c) Fe + CuSO₄ → FeSO₄ + Cu Explanation: Iron displaces copper (displacement) and it is also a redox reaction because iron is oxidised and copper ion is reduced.

Question 8

When fats and oils are kept in open containers for a long time, they develop an unpleasant smell and taste. This process is called rancidity. Which of the following methods can prevent rancidity? (a) Adding antioxidants (b) Flushing the container with nitrogen gas (c) Keeping the food in airtight containers (d) All of the above

Correct Answer: (d) All of the above Explanation: All three methods reduce contact with oxygen and prevent oxidation of fats and oils.

Question 9

A shiny brown coloured element ‘X’ on heating in air becomes black. On passing hydrogen gas over this black substance, it regains its original colour. Which of the following is correct? (a) X is iron and the black substance is Fe₂O₃ (b) X is copper and the black substance is CuO (c) The second reaction is a decomposition reaction (d) Copper is oxidised in the second reaction

Correct Answer: (b) X is copper and the black substance is CuO Explanation: Copper (shiny brown) forms black CuO on heating. In the second reaction, CuO is reduced back to copper.

Question 10

Which of the following reactions is endothermic in nature? (a) Burning of natural gas (b) Respiration (c) Reaction between barium hydroxide and ammonium chloride (d) Reaction between quick lime and water

Correct Answer: (c) Reaction between barium hydroxide and ammonium chloride Explanation: This reaction absorbs heat from the surroundings, making the test tube cold. It is endothermic.

Question 11

When lead nitrate is heated, brown fumes of nitrogen dioxide are evolved. This is an example of: (a) Combination reaction (b) Thermal decomposition reaction (c) Photochemical decomposition reaction (d) Displacement reaction

Correct Answer: (b) Thermal decomposition reaction Explanation: Lead nitrate decomposes on heating to form lead oxide, nitrogen dioxide and oxygen. It is a thermal decomposition reaction.

Question 12

In the reaction: ZnO + C → Zn + CO Which of the following statements is correct? (a) ZnO is oxidised and C is reduced (b) ZnO is reduced and C is oxidised (c) Both ZnO and C are oxidised (d) Both ZnO and C are reduced

Correct Answer: (b) ZnO is reduced and C is oxidised Explanation: ZnO loses oxygen (reduced) and carbon gains oxygen (oxidised). This is a redox reaction.

Case-Based Questions with Answers

Case 1: Whitewashing and Its Chemistry

Riya’s father decided to whitewash their house before Diwali. The painter used quick lime for this purpose. He mixed quick lime with water in a bucket. Riya observed that the mixture became hot and a hissing sound was produced. After applying it on the walls, the walls looked dull. However, after 2–3 days, the walls developed a shiny finish.

Q1. Which substance is used for whitewashing? (a) Calcium hydroxide (b) Calcium oxide (c) Calcium carbonate (d) Calcium chloride

Answer: (b) Calcium oxide Explanation: Quick lime (Calcium oxide) is used for whitewashing.

Q2. Why did the mixture become hot when quick lime was mixed with water? (a) It is an endothermic reaction (b) It is an exothermic combination reaction (c) It is a decomposition reaction (d) It is a displacement reaction

Answer: (b) It is an exothermic combination reaction Explanation: Quick lime reacts with water to form slaked lime and releases a large amount of heat.

Q3. What is the chemical name of the substance responsible for the shiny finish on the walls after 2–3 days? (a) Calcium hydroxide (b) Calcium oxide (c) Calcium carbonate (d) Calcium bicarbonate

Answer: (c) Calcium carbonate Explanation: Calcium hydroxide slowly reacts with CO₂ in air to form a thin layer of calcium carbonate, which gives a shiny finish.

Q4. The reaction between substance ‘Y’ (formed after mixing quick lime with water) and carbon dioxide is an example of: (a) Decomposition reaction (b) Displacement reaction (c) Combination reaction (d) Double displacement reaction

Answer: (c) Combination reaction Explanation: It is a combination reaction as two substances combine to form a single product (CaCO₃).

Case 2: Rancidity and Food Preservation

During summer vacation, Aarav noticed that the packet of chips he bought last month had developed a bad smell and taste. His mother told him that this happens due to rancidity. She advised him to always check the manufacturing date and also told him that manufacturers flush nitrogen gas in chip packets to prevent this problem.

Q1. What is the main cause of rancidity in food items containing fats and oils? (a) Reduction reaction (b) Oxidation reaction (c) Decomposition reaction (d) Combination reaction

Answer: (b) Oxidation reaction Explanation: Rancidity occurs due to the oxidation of fats and oils when exposed to air.

Q2. Why do manufacturers flush nitrogen gas in packets of chips and other fried food items? (a) Nitrogen increases the shelf life by preventing oxidation (b) Nitrogen makes the chips crispy (c) Nitrogen reacts with fats to improve taste (d) Nitrogen prevents decomposition of chips

Answer: (a) Nitrogen increases the shelf life by preventing oxidation Explanation: Nitrogen is inert and prevents contact of chips with oxygen, thus preventing rancidity.

Q3. Which of the following methods can be used to prevent rancidity? (a) Adding antioxidants (b) Storing food in airtight containers (c) Flushing packets with nitrogen gas (d) All of the above

Answer: (d) All of the above Explanation: All these methods reduce the oxidation of fats and oils.

Q4. Rancidity is an example of which type of reaction? (a) Endothermic reaction (b) Exothermic reaction (c) Oxidation reaction (d) Photochemical reaction

Answer: (c) Oxidation reaction Explanation: Rancidity is caused due to oxidation of fats and oils.

Assertion-Reason Questions with Answers

Directions: (a) Both A and R are true and R is the correct explanation of A. (b) Both A and R are true but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true.

Q1. Assertion (A): Magnesium ribbon should be cleaned with sandpaper before burning. Reason (R): Magnesium reacts with oxygen in air to form a protective layer of magnesium oxide.