✨ Hydrogen – Practice Set (Class 8, ICSE) 🔹
MCQs (12) Q1. The symbol of hydrogen is:
a) H₂
b) H
c) Hy
d) He
👉
Answer: b) H
Q2. Atomic number of hydrogen is:
a) 0
b) 1
c) 2
d) 3
👉
Answer: b) 1
Q3. Hydrogen was discovered by:
a) Cavendish
b) Lavoisier
c) Boyle
d) Rutherford
👉
Answer: a) Cavendish
Q4. Hydrogen is collected over:
a) Mercury
b) Water
c) Oil
d) Alcohol
👉
Answer: b) Water
Q5. Which property makes hydrogen different from other gases?
a) It is heavier than air
b) It is the lightest gas
c) It is poisonous
d) It has color
👉
Answer: b) It is the lightest gas
Q6. Reaction of Zn with dilute HCl gives:
a) ZnO
b) ZnCl₂ + H₂
c) Zn(OH)₂
d) Zn + Cl₂
👉
Answer: b) ZnCl₂ + H₂
Q7. Hydrogen is:
a) Combustible
b) Supporter of combustion
c) Both a & b
d) Neither a nor b
👉
Answer: a) Combustible
Q8. In the sun, hydrogen atoms fuse to form:
a) Oxygen
b) Helium
c) Nitrogen
d) Carbon
👉
Answer: b) Helium
Q9. The process of converting oils to ghee using hydrogen is called:
a) Hydrolysis
b) Hydrogenation
c) Oxidation
d) Sublimation
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Answer: b) Hydrogenation
Q10. Hydrogen is used in Haber’s process to make:
a) HCl
b) NH₃
c) H₂SO₄
d) CH₄
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Answer: b) NH₃
Q11. Which of the following metals react with dilute acids to produce hydrogen?
a) Copper
b) Zinc
c) Silver
d) Gold
👉
Answer: b) Zinc
Q12. Hydrogen is:
a) Metallic element
b) Non-metal
c) Metalloid
d) Noble gas
👉
Answer: b) Non-metal
🔹 Short Answer (8)
Q13. Why is hydrogen called the lightest element?
👉 Answer: Because it has only one proton and one electron, with atomic mass = 1.
Q14. Write one physical property of hydrogen.
👉 Answer: Hydrogen is colorless, odorless, tasteless, and the lightest gas.
Q15. Why is hydrogen not filled in modern balloons?
👉 Answer: Because it is highly inflammable and dangerous.
Q16. Name two natural sources of hydrogen.
👉 Answer: Water (H₂O) and natural gas (CH₄).
Q17. Write the chemical equation for the reaction of Zn with HCl.
👉 Answer:
Zn + 2HCl \rightarrow ZnCl_2 + H_2 ↑
Q18. Which metal is commonly used in the lab preparation of hydrogen and why?
👉 Answer: Granulated zinc, because it reacts steadily with dilute HCl or H₂SO₄.
Q19. Write one industrial use of hydrogen.
👉 Answer: Manufacture of ammonia (Haber’s process).
Q20. What happens when hydrogen burns in oxygen?
👉 Answer: It forms water and releases a large amount of energy.
2H_2 + O_2 \rightarrow 2H_2O + \text{energy}
🔹 Long Answer (6)
Q21. Explain the laboratory preparation of hydrogen with a diagram.
👉 Answer: Use Woulf’s bottle, zinc granules + dilute HCl. Gas collected over water. Equation:
Zn + 2HCl \rightarrow ZnCl_2 + H_2 ↑
Q22. State three chemical properties of hydrogen.
👉 Answer:
- Burns in oxygen to form water.
- Reduces metallic oxides to metals.
- Combines with nitrogen to form ammonia.
Q23. Why is hydrogen called a clean fuel?
👉 Answer: Because its combustion produces only water, no harmful gases like CO₂ or SO₂.
Q24. Explain the role of hydrogen in hydrogenation of oils.
👉 Answer: Unsaturated oils are heated with hydrogen in the presence of nickel catalyst to form saturated fats (vanaspati ghee).
Q25. Compare hydrogen with oxygen (any 3 points).
👉 Answer:
- Hydrogen is lighter; oxygen is heavier than air.
- Hydrogen burns; oxygen supports burning.
- Hydrogen atomic number = 1; oxygen atomic number = 8.
Q26. Why is hydrogen not considered a good fuel for daily use, though it has high calorific value?
👉 Answer: Because it is difficult to store, highly inflammable, and requires special cylinders.
🔹 Diagram / Activity Based (4
Q27. Draw a neat diagram of the laboratory preparation of hydrogen and label:
- Woulf’s bottle
- Delivery tube
- Water trough
- Gas jar
Q28. Show by a word equation and diagram how hydrogen reduces CuO to copper.
👉 Answer:
CuO + H_2 \xrightarrow{heat} Cu + H_2O
Q29. Draw the atomic structure of hydrogen.
👉 Answer: One proton in nucleus, one electron revolving.
Q30. Activity: How will you prove that hydrogen is lighter than air?
👉 Answer: Fill a soap bubble with hydrogen, it rises upward, showing hydrogen is lighter than air. (Diagram: bubble floating upward).
Q 31 .Give a Test to differentiate between jar containing pure hydrogen and other hydrogen air mixture
Ans
Flame (“pop”) test
You need: test tubes, stoppers, delivery tube, water trough (optional), lighter/taper, safety screen & goggles.
1. Take a small sample from the jar
Displace water into an inverted test tube (or fill a test tube from the jar and stopper it). Testing a small sample is far safer than testing the whole jar.
2. Bring a lighted splint to the mouth of the (inverted) test tube and very slightly unstopper it so the gas meets air at the mouth.
3. Observe:
Pure hydrogen: burns quietly with a pale blue flame at the mouth of the tube. No bang; the flame “licks” at the opening because mixing with oxygen happens only at the rim. The burning splint itself is extinguished inside the gas (H₂ doesn’t support combustion).
Hydrogen–air mixture (within explosive range ~4–75% H₂ in air): gives a sharp ‘pop’/small puff or even a mini explosion as the mixture ignites throughout the tube. You may see a mist of water droplets form (product water).
(Reaction: 2 H₂ + O₂ → 2 H₂O)
Why it works (quick intuition)
Pure H₂ is combustible but not a supporter of combustion. It only burns where it can mix with oxygen—i.e., at the tube mouth—so it’s gentle.
A pre-mixed H₂ + air sample already contains oxygen in the right proportions; ignition triggers rapid combustion everywhere in the sample → the characteristic ‘pop’.
Launch your Graphy