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Class 9 Science: Exploring Mixtures and their Separation, 8 practice questions with answers

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These are 8 practice questions on Chapter 5, Exploring Mixtures and their Separation, of the new NCERT Class 9 Science textbook, Exploration (First Edition, April 2026). Each has a worked answer and the textbook page it comes from. They cover the three percentage ways of giving a concentration, working back from a concentration, solubility and a saturated solution, choosing distillation, sublimation, and telling a colloid from a solution. Try each one on paper before you open the answer. How strong a mixture is, its concentration, is worked out in the Class 9 How Quantities Combine questions.

These questions are our own, drafted with AI help. Every number was re-computed by a test script and none of the numbers is taken from the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

What the chapter says you need

Facts from the NCERT textbook (Exploration: Textbook of Science for Grade 9, Chapter 5, printed pages 72 to 93):

Concentration

Question 1. 30.45 g of sugar is dissolved in 179.55 g of water. What is the concentration of the solution in mass by mass percentage?

Answer: 14.5 % m/m. Mass of solution = 30.45 + 179.55 = 210 g. Mass by mass percentage = 30.45 ÷ 210 × 100 = 14.5 % m/m. (Eq. 5.1 and Example 5.1, page 75.)

Question 2. 9.1 g of salt is dissolved in water to make 260 mL of solution. What is its mass by volume percentage?

Answer: 3.5 % m/v. Mass by volume percentage = 9.1 ÷ 260 × 100 = 3.5 % m/v. (Eq. 5.2, page 75.)

Question 3. 44.2 mL of alcohol is mixed with water to make 520 mL of solution. What is its volume by volume percentage?

Answer: 8.5 % v/v. Volume by volume percentage = 44.2 ÷ 520 × 100 = 8.5 % v/v. (Eq. 5.3, page 76.)

Question 4. A cleaning solution is 7.5 % m/m of a chemical. How many grams of the chemical are there in 430 g of the solution?

Answer: 32.25 g. 7.5 % m/m means 7.5 g in every 100 g of solution, so the mass of the chemical = 7.5 ÷ 100 × 430 = 32.25 g. (Eq. 5.1, page 75.)

Solubility and separation

Question 5. At a certain temperature, the solubility of a salt is 43 g per 100 g of water. What is the most salt that 275 g of water can dissolve at that temperature, and what is the solution then called?

Answer: 118.25 g; a saturated solution. 100 g of water dissolves at most 43 g, so 275 g of water dissolves at most 43 × 275 ÷ 100 = 118.25 g. A solution that cannot dissolve any more solute at that temperature is a saturated solution. (Solubility, page 76.)

Question 6. Two miscible liquids are mixed: liquid P boils at 104 °C and liquid Q at 121 °C. Can simple distillation separate them well? If not, which method does the textbook name for such a mixture?

Answer: no; fractional distillation. Their boiling points differ by only 121 − 104 = 17 °C, less than the 25 °C or so that simple distillation needs (page 80). The textbook separates components with such small differences in boiling point by fractional distillation, as in a petroleum refinery (page 81).

Question 7. A mixture contains common salt and naphthalene. How can the naphthalene be separated?

Answer: by sublimation. On heating, naphthalene changes directly into vapour, which is collected and turns back into a solid on cooling; the salt does not sublime and stays behind. The textbook names naphthalene as a substance that sublimes, like camphor. (Sublimation, page 84.)

Question 8. A narrow beam of light is passed through two liquids. In liquid X the path of the beam is clearly visible, and the particles do not settle even after a long time. In liquid Y the path cannot be seen. Which one is a colloid, and which is more likely a solution?

Answer: X is a colloid; Y is a solution. Colloid particles are large enough to scatter light, which makes the path of the beam visible (the Tyndall effect), but they stay spread out and do not settle. The particles in a solution are too small to scatter light, so the path is not seen. (Colloids, page 87; the Tyndall effect, pages 87 and 88.)

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Sources

All opened and read on 21 October 2026. Page numbers are the printed page numbers of the textbook; printed page = PDF page + 71.

The definitions, equations and rules are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.