Based on those trends and how important these topics are in the syllabus, we've put together a list of questions that are most likely to appear again in the upcoming exam. These predictions aren’t just guesses—they’re based on how often these questions show up and how CBSE usually frames its papers.
Here's a chart showing how often different types of chemical reactions appeared in recent CBSE papers, based on the previous year paper analysis:
Take a look below to see which types of questions you should definitely be ready for, with examples from previous papers to guide your practice.
Key Questions
Q1: (A) Write the essential conditions for the following reaction to take place and name its types: 2AgCl → 2Ag + Cl2
(B) What is observed when silver chloride is exposed to sunlight? Give the type of reaction involved.
Note: This is a key question and often appears in exams—understand it well.
Sunlight is essential for the above reaction to take place. This is a decomposition reaction. Such reactions require energy either in the form of heat, light or electricity for breaking down the reactants. Silver chloride turns grey after its decomposition into silver and chlorine by sunlight. This reaction is used in black and white photography. (B) When silver chloride is exposed to sunlight, it decomposes to form silver metal and chlorine gas. 2AgCl(s) → 2Ag(s) + Cl2(g) This is a photochemical decomposition reaction.
Q2: Assertion (A): Silver salts are used in black-and-white photography. Reason (R): Silver salts do not decompose in the presence of light. (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.
Ans: (c) Sol: Silver salt (AgCl) are used in black and white photography. Silver salt (AgCl) is photosensitive compound, it decomposes into elemental chlorine (Cl2) and Ag(metal). AgBr is also used as black and white photography.
Q3: Complete the following chemical reaction in the form of a balanced equation:
(B)
Q4: Translate the following statement into a balanced chemical equation : "Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate."
Q5: Take 3 g of barium hydroxide in a test tube. Now add about 2 g of ammonium chloride and mix the contents with the help of a glass rod. Now touch the test tube from outside. (i) What do you feel about touching the test tube? (ii) State the inference about the type of reaction that occurred. (iii) Write the balanced chemical equation of the reaction involved.
Ans:(i) On touching the test tube from outside, you will feel the test tube becoming cold. (ii) The inference about the type of reaction that occurred is that it is an endothermic reaction. In endothermic reactions, heat is absorbed from the surroundings, resulting in a decrease in temperature (iii) The balanced chemical equation for the reaction is: Ba(OH)2(s) + 2NH4Cl(s) → BaCl2(aq) + 2NH3(g) + 2H2O(l)
Q6: Write a chemical equation for the chemical reaction that occurs when the aqueous solutions of barium chloride and sodium sulphate react together. Write the symbols of the ions present in the compound precipitated in the reaction.
Q7: The emission of brown fumes in the given experimental set-up is due to:
(a) thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide. (b) thermal decomposition of lead nitrate which produces brown fumes of lead oxide. (c) oxidation of lead nitrate forming lead oxide and nitrogen dioxide. (d) oxidation of lead nitrate forming lead oxide and oxygen.
Note: This is a key question and often appears in exams—understand it well.
Ans: (a) When lead nitrate is heated, it undergoes thermal decomposition, resulting in the formation of lead oxide,PbO (a yellow solid), nitrogen dioxide NO2 (a brown gas), and oxygen, O2. The brown fumes observed in this setup are due to the release of nitrogen dioxide gas. The reaction is as follows:
Thus, the correct answer is (a) thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide.
Q8: What happens when food materials containing fats and oils are left for a long time? List two observable changes and suggest three ways by which this phenomenon can be prevented.
Ans: Food materials containing fats and oils change when left for a long time due to a process called rancidity. This occurs when air interacts with these substances, affecting their smell and taste. The observable changes include:
The food develops an unpleasant smell.
The taste of the food becomes off or stale.
To prevent rancidity, consider these methods:
Vacuum packing to limit air exposure.
Refrigeration to slow down oxidation.
Storing food away from direct sunlight to reduce heat exposure.
(A) Name the process depicted in the diagram. (B) Write the composition of gases collected at the anode and cathode. (C) Write the balanced chemical equation of the reaction taking place in this case. (D) The reaction does not take place if a few drops of dilute sulphuric acid are not added to water. Why?
Note: This is a key question and often appears in exams—understand it well.
Ans: (A)Electrolytic decomposition of water/ electrolysis of water. (B)The gas collected at cathode is hydrogen which is double the volume of oxygen collected at anode. (C) The balanced chemical equation for the reaction is:(D) The reaction does not occur without dilute sulphuric acid because:
Water is a poor conductor of electricity.
Adding sulphuric acid improves conductivity, allowing the reaction to proceed.
Q10: You might have noted that when copper powder is heated in a China dish, the reddish-brown surface of copper powder becomes coated with a black substance. (a) Why has this black substance formed? (b) What is the black substance? (c) Write the chemical equation of the reaction that takes place. (d) How can the black coating on the surface be turned reddish-brown?
Ans: (a) The black substance is formed because copper reacts with oxygen in the air to form copper oxide. (b) The black substance is copper oxide (CuO). (c) The chemical equation for the reaction is: 2Cu(s) + O2(g) → 2CuO(s) (d) The black coating on the surface can be turned reddish-brown by reducing it back to copper. This can be done by passing hydrogen gas over the hot copper oxide. The chemical equation for this reaction is: CuO(s) + H2(g) → Cu(s) + H2O(g) The reduction reaction converts the black copper oxide back to reddish-brown copper.
Q11: (a) A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction. (b) Ferrous sulfate, when heated, decomposes with the evolution of a gas having a characteristic odor of burning sulfur. Write the chemical reaction involved and identify the type of reaction.
Ans: (a) The chemical reaction involved is a double displacement reaction or a precipitation reaction. The reaction between potassium chloride (KCl) and silver nitrate (AgNO3) produces silver chloride (AgCl), which is an insoluble white substance. The balanced chemical equation for this reaction is: KCl(aq) + AgNO3(aq) → AgCl(s) + KNO3(aq) (b) The chemical reaction involved is a thermal decomposition reaction. Ferrous sulfate (FeSO4) when heated decomposes to form ferric oxide (Fe2O3), sulfur dioxide (SO2), and water (H2O). The balanced chemical equation for this reaction is: FeSO4(s) → Fe2O3(s) + SO2(g) + H2O(g)
Q12: What is a reduction reaction? Identify the substances that are oxidised and the substances that are reduced in the following reactions. (A) Fe2O3 + 2Al → Al2O3 + 2Fe (B) 2PbO + C → 2Pb + CO2
Ans: A reduction reaction is a reaction in which hydrogen is added to a substance or oxygen is removed from a substance. (A) In this reaction, Fe2O3 is losing oxygen and forming Fe, whereas Al is gaining oxygen and forming Al2O3. Therefore, Fe2O3 is getting reduced and Al is getting oxidised. (B) In this reaction, PbO is losing oxygen and forming Pb whereas C is gaining oxygen and forming CO. Therefore, PbO is getting reduced and C is getting oxidised.
Q13: (A) Identify the reducing agent in the following reactions: (i) 4NH3 + 5O2 → 4NO + 6H2O (ii) H2O + F2 → HF + HOF (iii) Fe2O3 + 3CO → 2Fe + 3CO2 (iv) 2H2 + O2 → 2H2O (B) Define a redox reaction in terms of gain or loss of oxygen.
Ans: (A)(i) NH3 is the reducing agent because it gets oxidised to NO by the removal of hydrogen and addition of oxygen. O2 has been reduced to H2O by the addition of hydrogen. (ii) H2O is the reducing agent. Here, F2 gets reduced to HF (addition of hydrogen) and H2O gets oxidised to HOF (removal of hydrogen). (iii)CO is the reducing agent. Here, CO has been oxidised to CO2 by the addition of oxygen. Fe2O3 has been reduced to Fe by the removal of oxygen. (iv) H2 is the reducing agent as it gets oxidised to H2O by the addition of oxygen. O2 has been reduced to H2O by the addition of hydrogen. (B) The reaction in which one element gets oxidised or addition of oxygen occurs and other element gets reduced or removal of oxygen occurs in other element is called redox reaction. Example:
Q14: In the experimental setup given below, it is observed that on passing the gas produced in the reaction in the solution ‘X’ the solution ‘X’ first turns milky and then colourless.
The option that justifies the given observation is that ‘X’ is aqueous calcium hydroxide and: (a) it turns milky due to carbon dioxide gas liberated in the reaction and after some time it becomes colourless due to the formation of calcium carbonate. (b) it turns milky due to the formation of calcium carbonate and on passing excess of carbon dioxide it becomes colourless due to the formation of calcium hydrogen carbonate which is soluble in water. (c) it turns milky due to the passing of carbon dioxide through it. It turns colourless as on further passing carbon dioxide, sodium hydrogen carbonate is formed which is soluble in water. (d) the carbon dioxide liberated during the reaction turns lime water milky due to the formation of calcium hydrogen carbonate and after some time, it turns colourless due to the formation of calcium carbonate which is soluble in water.
Note: This is a key question and often appears in exams—understand it well.
Ans: (b) When carbon dioxide is passed through aqueous calcium hydroxide (lime water), it initially reacts to form calcium carbonate, which is insoluble in water and causes the solution to turn milky:However, when excess carbon dioxide is passed through the solution, the calcium carbonate further reacts with the carbon dioxide and water to form calcium hydrogen carbonate, which is soluble in water, causing the solution to become clear again:
Thus, the correct answer is (b).
Q15: (a) Define a double displacement reaction. (b) Write the chemical equation of a double displacement reaction which is also a (i) Neutralisation reaction and (ii) Precipitation reaction. Give justification for your answer.
(a) The chemical reaction in which two reactants exchange ions to form two new compounds is called a double displacement reaction. (b) (i) When an aqueous solution of an acid reacts with a base (alkali) by exchanging their ions/radicals to form salt and water as the only products, the reaction which takes place is called neutralisation reaction. (ii) When the aqueous solutions of two ionic compounds react by exchanging their ions/radicals, to form two or more new compounds such that one of the products formed is an insoluble salt, and hence forms precipitate, the double displacement reaction is said to be precipitation reaction. When lead nitrate solution is mixed with potassium iodide solution, a yellow precipitate is formed. This reaction is a precipitation reaction and can be expressed as follows:
Important Topics for Preparation
Based on the analysis, the following topics are critical for CBSE Class 10 students preparing for "Chemical Reactions and Equations":
Types of Chemical Reactions
1. Combination: Understand reactions forming a single product e.g., CaO + H₂O → Ca(OH)₂
2. Decomposition: Focus on:
Thermal: FeSO₄ → Fe₂O₃ + SO₂ + SO₃
Photochemical: AgCl → Ag + Cl₂
Electrolytic: 2H₂O → 2H₂ + O₂
3. Displacement: Learn the reactivity series to predict outcomes e.g., Zn + CuSO₄ → ZnSO₄ + Cu
Practice Observations: Know key signs like color changes, gases, and precipitates
Solve Previous Year Papers: Especially from 2019–2024
Learn Practical Setups: Electrolysis, thermal decomposition, etc.
The document Sure Shot Questions for Board Exams: Chemical Reactions and Equations | Science Class 10 is a part of the Class 10 Course Science Class 10.
FAQs on Sure Shot Questions for Board Exams: Chemical Reactions and Equations - Science Class 10
1. What are chemical reactions and why are they important?
Ans.Chemical reactions are processes in which substances, known as reactants, undergo a transformation to form new substances called products. They are important because they are fundamental to all biological and chemical processes, including digestion, energy production, and the creation of new materials.
2. How can we represent chemical reactions using equations?
Ans.Chemical reactions can be represented using chemical equations, which show the reactants on the left side and the products on the right side, separated by an arrow. The equation must be balanced, meaning the number of atoms of each element is the same on both sides.
3. What are the different types of chemical reactions?
Ans.There are several types of chemical reactions including synthesis (combination), decomposition, single replacement, double replacement, and combustion. Each type of reaction has distinct characteristics and mechanisms.
4. How do you balance a chemical equation?
Ans.Balancing a chemical equation involves adjusting the coefficients of the reactants and products to ensure that the number of atoms for each element is the same on both sides of the equation. This process often requires trial and error and an understanding of the law of conservation of mass.
5. What role do catalysts play in chemical reactions?
Ans.Catalysts are substances that speed up chemical reactions without being consumed in the process. They work by lowering the activation energy required for the reaction to occur, allowing it to proceed more quickly and efficiently.
(A) Name the process depicted in the diagram. (B) Write the composition of gases collected at the anode and cathode. (C) Write the balanced chemical equation of the reaction taking place in this case. 
(D) The reaction does not occur without dilute sulphuric acid because:
However, when excess carbon dioxide is passed through the solution, the calcium carbonate further reacts with the carbon dioxide and water to form calcium hydrogen carbonate, which is soluble in water, causing the solution to become clear again:
Thus, the correct answer is (b).
(ii) 
