CBSE Class 10 Science · Ch 1: Chemical Reactions and Equations

Topics in this test

Difficulty: 3 easy · 8 medium · 19 hard

Sample questions with answers

The first 5 questions of this free test.

1. Q1. A manufacturer packs potato chips in bags that are flushed with nitrogen gas before sealing. The main purpose of doing this is to:

   • A. Supply oxygen that keeps the food fresh for longer
   • B. Speed up the oxidation of the oil to improve the taste
   • C. Add moisture so that the chips stay soft and crisp
   • D. Remove oxygen so that the oily food does not get oxidised and turn rancid
   Solution

   Nitrogen is unreactive and pushes out oxygen, so the oily food cannot get oxidised; this prevents rancidity and keeps the chips fresh.

2. Q2. Consider the following statements: (i) A combination reaction can be exothermic. (ii) A decomposition reaction is essentially the opposite of a combination reaction. (iii) Respiration in our body is an endothermic process. Which of the statements are correct?

   • A. (i), (ii) and (iii)
   • B. (i) and (ii) only
   • C. (i) and (iii) only
   • D. (ii) and (iii) only
   Solution

   Combination reactions often release heat and decomposition is the reverse of combination, so (i) and (ii) are correct; respiration releases energy, so it is exothermic, making (iii) wrong.

3. Q3. Three of the following reactions belong to the same type. Which one is the odd one out?

   • A. $2H_2O \xrightarrow{\text{electricity}} 2H_2 + O_2$
   • B. $CaCO_3 \xrightarrow{\Delta} CaO + CO_2$
   • C. $CaO + H_2O \rightarrow Ca(OH)_2$
   • D. $2AgCl \xrightarrow{\text{sunlight}} 2Ag + Cl_2$
   Solution

   The other three are decomposition reactions (one substance breaking up), but $CaO + H_2O \rightarrow Ca(OH)_2$ is a combination reaction where two substances join.

4. Q4. Match each reaction type in Column I with the correct example in Column II: Column I: (P) Decomposition (Q) Displacement (R) Double displacement Column II: (1) $Zn + 2HCl \rightarrow ZnCl_2 + H_2$ (2) $CaCO_3 \xrightarrow{\Delta} CaO + CO_2$ (3) $Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl$ The correct matching is:

   • A. P-3, Q-1, R-2
   • B. P-2, Q-1, R-3
   • C. P-2, Q-3, R-1
   • D. P-1, Q-2, R-3
   Solution

   $CaCO_3$ breaks into simpler substances (decomposition), zinc displaces hydrogen (displacement), and sulphate and chloride ions are exchanged (double displacement).

5. Q5. Assertion (A): White silver chloride turns grey when left in sunlight. Reason (R): Silver chloride undergoes a photolytic decomposition reaction to give silver and chlorine. Choose the correct option:

   • A. Both A and R are true, but R is not the correct explanation of A
   • B. A is false, but R is true
   • C. Both A and R are true, and R is the correct explanation of A
   • D. A is true, but R is false
   Solution

   In sunlight $2AgCl \rightarrow 2Ag + Cl_2$; the grey colour is the silver formed, so both A and R are true and R correctly explains A.

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