Nature of Matter: Elements, Compounds, and Mixtures — Hard

Q1. Two substances A and B combine to form a product C: A + B → C. A and B cannot be broken down into simpler substances by chemical reactions. Which statement is correct?

• A. A, B and C are all compounds and only C has a fixed composition.
• B. C is a compound and A and B have a fixed composition.
• C. A and B are compounds and C has a fixed composition.
• D. A and B are elements, C is a compound, and has a fixed composition.

Q2. Assertion (A): Air is a mixture. Reason (R): A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

• 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.

Q3. From the chapter exercise list — aluminium, rust, glucose, seawater, sulfur, hydrogen, baking soda — which set is correctly classified?

• A. Elements: rust, glucose; Compounds: aluminium, sulfur
• B. Elements: aluminium, sulfur, hydrogen; Compounds: rust, glucose, baking soda; Mixture: seawater
• C. Elements: glucose, baking soda; Compounds: hydrogen, sulfur
• D. Mixture: aluminium, sulfur; Compound: seawater

Q4. Consider the following statements about Sample B (iron sulfide) in Activity 8.5: I. Its texture and colour are the same throughout. II. A magnet attracts iron filings out of it. III. Its properties differ completely from iron and sulfur. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q5. From Activity 8.3, the inference Water → Hydrogen + Oxygen establishes that water is a

• A. Element, because the gases collected are also elements
• B. Compound, because it splits into two different elements by chemical means
• C. Mixture, because two gases came out of it
• D. Pure element that contains hydrogen and oxygen as impurities

Q6. Iron reacts with moist air to form iron oxide; magnesium burns in oxygen to form magnesium oxide. In the two reactions taken together, the substances are correctly classified as

• A. Iron, magnesium, oxygen — elements; moist air — mixture; iron oxide, magnesium oxide — compounds
• B. All six substances — elements
• C. Iron oxide and magnesium oxide — mixtures; rest — elements
• D. Moist air, iron oxide, magnesium oxide — elements; iron, magnesium, oxygen — compounds

Q7. Consider the following statements about mixtures: I. The components of a mixture must be pure substances in science. II. The components of a mixture do not react chemically with each other. III. The components of a mixture always exist in a fixed ratio. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three

Q8. In Fig. 8.24 (Exercise Q10), iron filings are reacted with dilute hydrochloric acid and a colourless gas A is collected at the mouth of the test tube. Gas A is most likely

• A. Oxygen
• B. Hydrogen sulfide
• C. Carbon dioxide
• D. Hydrogen

Q9. A student claims that any substance that cannot be separated by physical processes like filtration or evaporation is a pure substance. Based on the chapter, this claim is

• A. Wholly correct — physical separation is the only test
• B. Correct in direction but pure substances can still be elements or compounds
• C. Wrong — pure substances can always be separated physically
• D. Wrong — only compounds count as pure substances

Q10. Engineers prefer stainless steel over pure iron for utensils and many building parts. The best chapter-based reason is

• A. Stainless steel is a pure element and pure iron is a compound
• B. Stainless steel is an alloy that is stronger and more durable than pure iron
• C. Pure iron cannot be made into thin sheets
• D. Stainless steel is cheaper than every form of iron

Q11. If the oxygen fraction in air were replaced entirely by nitrogen, which two everyday processes would be most directly affected, according to the chapter?

• A. Photosynthesis and rusting
• B. Respiration and combustion
• C. Evaporation and condensation
• D. Lime-water turning milky and rainfall

Q12. Hydrogen is a fuel and oxygen supports combustion, yet water (made of hydrogen and oxygen) extinguishes fire. Which chapter principle does this best demonstrate?

• A. Components of a mixture retain their properties
• B. A compound's properties differ from the elements that form it
• C. Air is a uniform mixture
• D. Pure water is a strong conductor of electricity

Q13. The 'Our scientific heritage' box names Kamsya (bronze) as Copper (Tamra, 4 parts) + Tin (Vanga, 1 part). The ratio of copper to tin in this ancient bronze is therefore

• A. 1 : 4
• B. 1 : 1
• C. 4 : 1
• D. 2 : 3

Q14. In Activity 8.3, the test tube in which the flame of a burning candle glows brighter when brought near the mouth contains

• A. Hydrogen, because hydrogen makes flames brighter
• B. Oxygen, because oxygen supports combustion
• C. Carbon dioxide, because it stops the flame from dying
• D. Nitrogen, because nitrogen is inert

Q15. Consider the following statements about minerals: I. Most rocks are a mixture of minerals. II. Native minerals (e.g., gold, sulfur) are pure elements, not compounds. III. Quartz and calcite are pure elements. Which are correct?

• A. I and II only
• B. II and III only
• C. I and III only
• D. All three