CBSE Class 10 Science Chapter 1 Chemical Reactions and Equations Important Questions 2027

The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is (A) 1 : 1 (B) 2 : 1 (C) 4 : 1 (D) 1 : 2

C₆H₁₂O₆(aq) + 6O₂(g) -> 6CO₂(g) + 6H₂O(l). The above reaction is an example of - (A) Displacement Reaction (B) Endothermic Reaction (C) Exothermic Reaction (D) Neutralisation Reaction

Account for the following: (a) White silver chloride turns grey when exposed to sunlight. (b) Lead (II) nitrate on heating releases brown fumes. (c) Bags of oil and fat containing food items are flushed with nitrogen gas.

Which of the following equations represent redox reactions and what are the values for 'p' and 'q' in these equations? Equation 1: Fe₂O₃(s) + 2Al(s) -> Al₂O₃(s) + p Fe(l) + heat. Equation 2: 2C₄H₁₀(g) + 13O₂(g) -[heat]-> 8CO₂(g) + q H₂O(g). A. Only equation 1 is a redox reaction, p =1 and q=3 B. Both equations 1 and 2 are redox reactions, p= 2 and q=4 C. Only equation 2 is a redox reaction, p= 2 and q= 10 D. Both equations 1 and 2 are redox reactions, p= 2 and q=10

In the reaction of aqueous solution of barium chloride with aqueous solution of sodium sulphate, the aqueous solution formed will be: A. BaCl₂ B. BaSO₄ C. Na₂SO₄ D. NaCl

Amrita electrolysed distilled water using the set-up shown in figure 1. She was expecting two gases to be evolved at the anode and cathode respectively. Suddenly, she realised that the bulb in the circuit did not glow when she used distilled water (figure 2). After this realization, she added a substance to the distilled water for electrolysis to take place. Answer the following questions: A. Which gas was she expecting to be formed at the anode and which one at the cathode respectively? B. Why did the bulb not glow when Amrita passed electricity through distilled water? C. Which substance was added by Amrita to distilled water to get the expected result? (For visually impaired students: Identify the type of reaction: A. ZnO + C -> Zn + CO; B. ZnCO₃ -[heat]-> ZnO + CO₂; C. 2Mg + O₂ -> 2MgO + heat.)

Electrolysis of water is a decomposition reaction. The mass ratio (M_H : M_O) of hydrogen and oxygen gases liberated at the electrodes during electrolysis of water is : (A) 8 : 1 (B) 2 : 1 (C) 1 : 2 (D) 1 : 8

Assertion (A): Decomposition reactions are generally endothermic reactions. Reason (R): Decomposition of organic matter into compost is an exothermic process. Select the correct answer: (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.

A student performs the following experiment in his school laboratory (a conical flask fitted with a delivery tube containing dilute sulphuric acid and Zn granules - see figure). List two observations to justify that in this experiment a chemical change has taken place.

Identify 'p', 'q' and 'r' in the following balanced reaction: p Pb(NO₃)₂(s) --Heat--> q PbO(s) + r NO₂(g) + O₂(g) A. 2,2,4 B. 2,4,2 C. 2,4,4 D. 4,2,2

When 50g of lead powder is added to 300 ml of blue copper sulphate solution, after a few hours, the solution becomes colourless. This is an example of A. Combination reaction B. Decomposition reaction C. Displacement reaction D. Double displacement reaction

Which of the following is an endothermic reaction? A. Burning of candle. B. Cooking of food. C. Decomposition of Vegetable matter. D. Reaction of Sodium with air

Identify the type of each of the following reactions stating the reason for your answers. A. Fe₂O₃ + 2Al -> Al₂O₃ + 2Fe + heat B. Pb(NO₃)₂ + 2KI -> PbI₂(down-arrow) + 2KNO₃

When 2 mL of sodium hydroxide solution is added to few pieces of granulated zinc in a test tube and then warmed, the reaction that occurs can be written in the form of a balanced chemical equation as: (a) NaOH + Zn -> NaZnO₂ + H₂ (b) 2NaOH + Zn -> Na₂ZnO₂ + H₂ (c) 2NaOH + Zn -> NaZnO₂ + H₂ (d) 2NaOH + Zn -> Na₂ZnO₂ + H₂O

Select from the following a decomposition reaction in which source of energy for decomposition is light: (a) 2FeSO₄ -> Fe₂O₃ + SO₂ + SO₃ (b) 2H₂O -> 2H₂ + O₂ (c) 2AgBr -> 2Ag + Br₂ (d) CaCO₃ -> CaO + CO₂

MnO₂ + 4HCl -> MnCl₂ + 2H₂O + Cl₂. The reaction given above is a redox reaction because in this case: (a) MnO₂ is oxidised and HCl is reduced. (b) HCl is oxidised. (c) MnO₂ is reduced. (d) MnO₂ is reduced and HCl is oxidised.

Name the type of chemical reaction in which calcium oxide reacts with water. Justify your answer by giving balanced chemical equation for the chemical reaction.

Write one chemical equation each for the chemical reaction in which the following have taken place: (i) Change in colour (ii) Change in temperature (iii) Formation of precipitate. Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.

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. [Set-up shows lead nitrate being heated over a burner, giving off brown fumes.]

MnO₂ + x HCl -> MnCl₂ + y H₂O + z Cl₂. In order to balance the above chemical equation, the values of x, y and z respectively are: (a) 6, 2, 2 (b) 4, 1, 2 (c) 4, 2, 1 (d) 2, 2, 1

Write balanced chemical equation for the reaction that occurs when: (i) blue coloured copper sulphate crystals are heated and (ii) Sodium hydrogen carbonate is heated during cooking.

(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.