Question Bank — Nature of Matter: Elements, Compounds, and Mixtures

Section A — MCQs (10 questions, 1 mark each)

1. Which of the following is a uniform mixture?
   (a) Sprout salad (b) Poha (c) Sugar dissolved in water (d) Sand and water

2. In the electrolysis of water, the gas collected in larger volume is:
   (a) Hydrogen (b) Oxygen (c) Carbon dioxide (d) Nitrogen

3. Assertion (A): Air is considered a mixture.
   Reason (R): The components of air can be separated by physical processes and retain their individual properties.
   (a) Both A and R true, R explains A
   (b) Both A and R true, R does not explain A
   (c) A true, R false
   (d) A false, R true

4. Assertion (A): Water is a compound.
   Reason (R): The constituent elements of water cannot be separated by any physical method.
   (a) Both A and R true, R explains A
   (b) Both A and R true, R does not explain A
   (c) A true, R false
   (d) A false, R true

5. Which of the following statements is correct about elements?
   (a) Elements can be broken down into simpler substances by physical methods.
   (b) Elements are made up of identical particles called atoms.
   (c) All elements exist as gases at room temperature.
   (d) Elements always form mixtures when combined.

6. When iron filings and sulfur are mixed without heating, the resulting Sample A is:
   (a) A compound (b) A uniform mixture (c) A non-uniform mixture (d) An element

7. The black mass formed on heating iron filings with sulfur is:
   (a) Still attracted by a magnet (b) Iron sulfide, a compound (c) A mixture of iron and sulfur (d) An element

8. Which of the following is not a pure substance?
   (a) Oxygen (b) Gold (c) Seawater (d) Sugar

9. Dust particles in air are:
   (a) An integral component of air (b) Pollutants suspended in air (c) Uniformly distributed gases (d) Part of the compound air

10. Minerals are best described as:
    (a) Always pure elements (b) Natural solid substances with fixed chemical composition (c) Only mixtures (d) Only compounds formed in laboratories

Section B — Very Short Answer (6 questions, 2 marks each)

1. Define a mixture and give one example of a uniform mixture from daily life.
2. State two differences between elements and compounds.
3. Why is air classified as a uniform mixture?
4. What observation in Activity 8.1 confirms the presence of carbon dioxide in air?
5. Name the two gases produced when electricity is passed through water and state the ratio in which they are formed.
6. What is the difference between the behaviour of Sample A and Sample B when a magnet is brought near them?

Section C — Short Answer (5 questions, 3 marks each)

1. Explain why sugar is a compound and not an element, with reference to the heating experiment.
2. Distinguish between uniform and non-uniform mixtures with two examples of each.
3. Describe how the properties of iron sulfide (Sample B) differ from those of the original mixture of iron and sulfur.
4. Why are alloys considered mixtures rather than compounds? Give two examples.
5. Classify the following as element, compound or mixture: nitrogen, rust, baking soda, muddy water, sulfur. Give one reason for any two.

Section D — Long Answer (3 questions, 5 marks each)

1. Draw a neat labelled diagram of the setup used to show that water is a compound by passing electricity through it. Label the following: battery, test tubes, water containing dilute sulfuric acid, gases collected. State the observations and conclusions.
2. Explain with the help of an activity how heating a mixture of iron filings and sulfur leads to the formation of a compound. Compare the properties of the mixture and the compound formed.
3. “Pure substances are either elements or compounds.” Justify this statement using examples from the chapter. How does this differ from the common meaning of the word ‘pure’?

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1

A scientist mixes 5.6 g iron filings with 3.2 g sulfur powder on a watch glass and labels it Sample A. Half of this mixture is heated in a china dish until a black mass forms; this is labelled Sample B. When a magnet is passed over Sample A, particles are attracted, but no such attraction occurs with Sample B. On adding dilute HCl, Sample A releases a colourless, odourless gas that burns with a pop sound, while Sample B releases a gas with a rotten-egg smell.

Sub-questions:
(a) Identify Sample A and Sample B. (1 mark)
(b) Why does the magnet behave differently with the two samples? (1 mark)
(c) Write the word equations for the reactions of both samples with dilute HCl. (1 mark)
(d) What does this activity demonstrate about the difference between mixtures and compounds? (1 mark)

Case 2

Graphene aerogel, made from carbon, is described as the lightest material on Earth. It is highly porous and can absorb large quantities of oil, making it useful for cleaning oil spills. It is also used in energy-saving devices and special building coatings.

Sub-questions:
(a) To which category of matter does graphene aerogel belong? (1 mark)
(b) Why is it useful for cleaning oil spills? (1 mark)
(c) Name the element from which it is made and state whether it is a metal or non-metal. (1 mark)
(d) How does this example show the practical use of elements and compounds? (1 mark)

Section F — HOTS and Application (4 questions, 3 marks each)

1. Predict-and-justify: What would happen if water were a mixture of hydrogen and oxygen instead of a compound? How would this affect its use in extinguishing fire? Justify using properties of mixtures and compounds.
2. Analyse an unexpected observation: In the electrolysis activity, one test tube collected twice the volume of gas as the other. A student expected equal volumes. Analyse the observation and state what it indicates about the composition of water.
3. Apply the concept: A new material is developed that looks uniform, is not attracted by a magnet, and produces a gas with a distinct smell when treated with dilute acid. Apply your understanding of the iron-sulfur activity to decide whether this material is likely a mixture or a compound, and justify.
4. Compare two situations: In one case, iron filings and sulfur are simply mixed; in the other, they are heated together. Compare the two situations and justify which outcome differs and why, with reference to chemical combination.