mixtures MCQs for UPSC Prelims

26 practice questions on mixtures from the Nature of Matter: Elements, Compounds, and Mixtures section of the UPSC Prelims syllabus. 26 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

8 Easy 13 Medium 5 Hard

Sample questions

Q1
medium

Sea water contains several salts dissolved in water. Sea water is best described as

  1. A a substance with a fixed composition
  2. B an element
  3. C a compound
  4. D a mixture
Show answer and explanation

Correct answer: D - a mixture

Dissolved salts sit in the water without combining chemically with it, so sea water is a mixture. A compound would have its parts chemically joined, and an element would contain only one kind of particle. Sea water from different places contains different amounts of salt, so its composition is not fixed.

Q2
easy

Water with salt stirred into it still tastes salty. This shows that in a mixture

  1. A each substance keeps its own properties
  2. B a new substance with a new taste is formed
  3. C the substances lose their properties
  4. D the substances have combined chemically
Show answer and explanation

Correct answer: A - each substance keeps its own properties

The salty taste belongs to the salt, and it survives the mixing, so the salt has kept its properties. If the properties were lost, the water would taste plain. No new substance has appeared, and chemical combination would have destroyed the salty taste.

Q3
hard

Assertion (A): Salt dissolved in water is called a mixture rather than a compound. Reason (R): The salt and the water are not chemically combined, and each can be recovered unchanged.

  1. A Both A and R are true, and R is the correct explanation of A
  2. B Both A and R are true, but R is not the correct explanation of A
  3. C A is true, but R is false
  4. D A is false, but R is true
Show answer and explanation

Correct answer: A - Both A and R are true, and R is the correct explanation of A

Both statements are true. Salt water counts as a mixture precisely because no chemical combination has taken place and the salt can be got back by evaporation, so R is the reason behind A. The choice denying the link misses this, and neither statement is false.

Q4
easy

A mixture is formed when

  1. A a substance is cooled until it turns into a solid
  2. B two substances combine chemically to give a brand new substance
  3. C two or more substances are put together without combining chemically
  4. D a single substance is heated very strongly
Show answer and explanation

Correct answer: C - two or more substances are put together without combining chemically

In a mixture the substances simply sit together, each keeping what it is, with no chemical combination. Chemical combination gives a compound, not a mixture. Heating a single substance or cooling it only changes its state or breaks it down; it does not make a mixture.

Q5
medium

Sugar is stirred into water until it can no longer be seen. Is the result a mixture?

  1. A No, because a completely new substance has been formed
  2. B No, because the sugar can no longer be seen
  3. C Yes, because the sugar and the water are only mixed and have not combined chemically
  4. D Yes, because a chemical change has taken place between them
Show answer and explanation

Correct answer: C - Yes, because the sugar and the water are only mixed and have not combined chemically

The sugar is still sugar, as its taste shows and as evaporation would prove, so nothing has chemically combined and the result is a mixture. Being invisible is not the test; dissolved particles are always too small to see. No new substance has appeared, so no chemical change has occurred.

Q6
hard

A shopkeeper prepares a spice mix. Each batch contains a slightly different amount of chilli powder, yet every batch is still sold as the same spice mix. Why is this possible?

  1. A The spices lose their own properties as soon as they are mixed
  2. B Every batch is really a different compound
  3. C The spices combine chemically in a fixed ratio each time
  4. D The spices are only mixed together, and a mixture has no fixed proportion
Show answer and explanation

Correct answer: D - The spices are only mixed together, and a mixture has no fixed proportion

Mixing allows any proportion, so a slightly different amount of chilli still gives the same kind of mix, only a hotter or milder one. A fixed ratio would be required only if a compound were being made. Each spice keeps its own taste and smell, which is why the mix works at all.

Q7
medium

Which of these everyday materials is NOT a mixture?

  1. A The air around us
  2. B Distilled water
  3. C A fizzy cold drink
  4. D Garden soil
Show answer and explanation

Correct answer: B - Distilled water

Distilled water has had everything else removed, so only one substance remains. Soil holds sand, clay, humus and water together. A cold drink holds sugar and dissolved gas in water, and air holds several gases, so all three are mixtures.

Q8
medium

Why is muddy river water described as a heterogeneous mixture?

  1. A The water has become a new pure substance
  2. B The mud dissolves completely and disappears
  3. C The mud has combined chemically with the water
  4. D The mud particles are not spread evenly and can be seen in the water
Show answer and explanation

Correct answer: D - The mud particles are not spread evenly and can be seen in the water

Visible, unevenly spread mud is exactly what makes a mixture heterogeneous. No chemical combination happens between mud and water. If the mud truly dissolved, the water would look clear and the mixture would be homogeneous, and no new pure substance is formed.

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