Introduction
Chemical Reactivity is an important chapter of Class 9 Chemistry that explains how and why different substances undergo chemical reactions. This chapter focuses on the reactivity of metals and non-metals, the reactivity series, displacement reactions, and the factors that influence the ability of elements to react. Understanding chemical reactivity helps students predict whether a chemical reaction will occur and what products may be formed.
Students learn how metals are arranged according to their reactivity and why highly reactive metals such as potassium and sodium react more easily compared to less reactive metals such as gold and silver. The chapter also explains how electronic configuration, position in the periodic table, and chemical properties affect the behaviour of elements. Concepts such as displacement reactions and reactions of metals with acids and water provide a strong foundation for understanding advanced Chemistry topics.
On this page, you will find carefully selected Class 9 Chemistry Chapter 8 MCQs with answers and explanations, along with learning outcomes, quick revision notes, important definitions, important chemical equations, exam tips, and common mistakes to help you prepare effectively for school and board examinations.
Learning Outcomes
After studying this chapter, students will be able to:
- Explain the concept of chemical reactivity.
- Understand the reactivity series of metals.
- Compare reactive and less reactive metals.
- Predict displacement reactions using the activity series.
- Explain reactions of metals with water and acids.
- Understand factors affecting chemical reactivity.
- Relate electronic configuration with chemical behaviour.
Quick Notes – Chapter Summary
- Chemical reactivity describes how easily a substance undergoes a chemical reaction.
- The reactivity series arranges metals from most reactive to least reactive.
- Potassium and sodium are highly reactive metals.
- Gold and silver are among the least reactive metals.
- More reactive metals can displace less reactive metals from their compounds.
- Metals above hydrogen in the reactivity series can release hydrogen gas from acids.
- Metal reactivity depends on electronic configuration and tendency to lose electrons.
- Alkali metals are highly reactive because they easily lose one electron.
- Noble metals are less reactive and resist corrosion.
- Reaction conditions such as temperature and concentration can affect reaction rates.
Important Definitions
Chemical Reactivity: The tendency of a substance to undergo a chemical reaction.
Reactivity Series: An arrangement of metals according to their chemical reactivity from highest to lowest.
Displacement Reaction: A reaction in which a more reactive element replaces a less reactive element from its compound.
Activity Series: A list showing the relative reactivity of elements.
Reactive Metal: A metal that easily takes part in chemical reactions.
Noble Metal: A metal with very low reactivity that resists oxidation and corrosion.
Corrosion: The gradual damage of metals due to reactions with substances in the environment.
Important Chemical Equations
Reaction of Metal with Acid
Metal + Acid → Salt + Hydrogen Gas
Example:
Zn + 2HCl → ZnCl₂ + H₂
Reaction of Metal with Water
Metal + Water → Metal Hydroxide + Hydrogen Gas
Example:
2Na + 2H₂O → 2NaOH + H₂
Displacement Reaction
Zn + CuSO₄ → ZnSO₄ + Cu
Important Concepts
Prediction of chemical reactions.
Reactivity series of metals.
Activity of metals.
Displacement reactions.
Metals and acids.
Metals and water.
Highly reactive and less reactive metals.
Noble metals.
Effect of electronic configuration on reactivity.
Class 9 Chemistry Chapter 8 – Chemical Reactivity MCQs
1. What does the reactivity series of metals indicate?
- A. The order of atomic masses
- B. The order of metals based on their reactivity ✅
- C. The melting points of metals
- D. The density of metals
Explanation: The reactivity series arranges metals from most reactive to least reactive based on their chemical behavior.
2. Which metal is the most reactive in the reactivity series?
- A. Copper
- B. Zinc
- C. Potassium ✅
- D. Silver
Explanation: Potassium is highly reactive and reacts vigorously with water and oxygen.
3. What type of reaction occurs when a more reactive metal displaces a less reactive metal from its compound?
- A. Displacement reaction ✅
- B. Neutralization reaction
- C. Combination reaction
- D. Decomposition reaction
Explanation: In displacement reactions, a more reactive metal replaces a less reactive metal from its salt solution.
4. Which of the following metals will displace copper from copper sulfate solution?
- A. Zinc ✅
- B. Silver
- C. Gold
- D. Mercury
Explanation: Zinc is more reactive than copper and can displace it from copper sulfate solution.
5. Why does silver not react with dilute hydrochloric acid?
- A. Because it is a non-metal
- B. Because it is less reactive than hydrogen ✅
- C. Because it is insoluble
- D. Because it is unstable
Explanation: Metals less reactive than hydrogen cannot displace hydrogen from acids.
6. Which gas is produced when a reactive metal reacts with an acid?
- A. Oxygen
- B. Hydrogen ✅
- C. Carbon dioxide
- D. Nitrogen
Explanation: Reactive metals react with acids to produce hydrogen gas and a salt.
7. Which factor does NOT affect the chemical reactivity of metals?
- A. Position in the periodic table
- B. Electronic configuration
- C. Density ✅
- D. Reactivity series position
Explanation: Density is a physical property and does not directly determine reactivity.
8. Which metal is least reactive among the following?
- A. Magnesium
- B. Calcium
- C. Gold ✅
- D. Aluminium
Explanation: Gold is at the bottom of the reactivity series and does not corrode easily.
9. What is the main use of the reactivity series?
- A. To determine melting points
- B. To predict reaction feasibility ✅
- C. To calculate molar mass
- D. To determine hardness
Explanation: The reactivity series helps in predicting which metals can displace others in chemical reactions.
10. Why does potassium react explosively with water?
- A. Because it is a noble metal
- B. Because it is less dense than water
- C. Because it is highly reactive and releases heat rapidly ✅
- D. Because it dissolves completely
Explanation: Potassium reacts vigorously with water, producing hydrogen gas and heat, which ignites the hydrogen.
11. Which group of metals is the most reactive in the periodic table?
- A. Alkali metals ✅
- B. Transition metals
- C. Noble metals
- D. Alkaline earth metals
Explanation: Alkali metals are highly reactive because they easily lose their outermost electron.
12. Sodium is stored under oil because:
- A. It dissolves in oil
- B. It reacts quickly with air and moisture ✅
- C. It becomes harder in oil
- D. It changes colour in sunlight
Explanation: Sodium is highly reactive and is stored under oil to prevent reaction with oxygen and moisture.
13. Which metal is commonly protected from corrosion by galvanizing?
- A. Gold
- B. Silver
- C. Iron ✅
- D. Copper
Explanation: Galvanizing protects iron by coating it with a layer of zinc.
14. Rusting of iron requires:
- A. Nitrogen only
- B. Carbon dioxide only
- C. Oxygen and moisture ✅
- D. Hydrogen only
Explanation: Iron rusts when it reacts with oxygen and water present in the environment.
15. Which non-metal group is highly reactive?
- A. Noble gases
- B. Halogens ✅
- C. Alkali metals
- D. Transition metals
Explanation: Halogens are highly reactive non-metals because they need one electron to complete their outer shell.
16. Which metal is extracted from its ore using electrolysis because of its high reactivity?
- A. Copper
- B. Silver
- C. Aluminium ✅
- D. Gold
Explanation: Highly reactive metals like aluminium are extracted by electrolysis because they cannot be easily reduced by carbon.
17. The tendency of a metal to lose electrons is called:
- A. Reduction
- B. Oxidation tendency ✅
- C. Neutralization
- D. Condensation
Explanation: Reactive metals easily lose electrons and undergo oxidation.
18. Which of these metals is known as a noble metal?
- A. Sodium
- B. Calcium
- C. Magnesium
- D. Gold ✅
Explanation: Gold is called a noble metal because it is very unreactive and resists corrosion.
19. Reactivity of metals generally depends on their ability to:
- A. Lose electrons ✅
- B. Gain protons
- C. Increase atomic mass
- D. Change their nucleus
Explanation: Metals become reactive by easily losing valence electrons to form positive ions.
20. Which metal reacts with water to produce sodium hydroxide and hydrogen gas?
- A. Copper
- B. Sodium ✅
- C. Silver
- D. Gold
Explanation: Sodium reacts with water to form sodium hydroxide and hydrogen gas.
Exam Tips
- Memorize the order of common metals in the reactivity series.
- Understand why some metals displace others from solutions.
- Practice displacement reaction examples.
- Learn reactions of metals with acids and water.
- Focus on concepts instead of only memorizing reactions.
Common Mistakes
❌ Thinking all metals have the same reactivity.
❌ Confusing reactive metals with noble metals.
❌ Forgetting that less reactive metals cannot displace more reactive metals.
❌ Assuming all metals react with acids.
❌ Mixing up physical properties and chemical reactivity.
Conclusion
Chemical Reactivity helps students understand why substances react differently and how chemical reactions can be predicted. The reactivity series, displacement reactions, and reactions of metals with acids and water explain many important chemical processes. Learning these concepts builds a strong foundation for advanced Chemistry topics. Regular practice of MCQs, important definitions, and chemical equations will improve understanding and help students perform better in school and board examinations.