matter-is-made-of-particles MCQs for UPSC Prelims

27 practice questions on matter-is-made-of-particles from the Particulate Nature of Matter section of the UPSC Prelims syllabus. 27 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

8 Easy 14 Medium 5 Hard

Sample questions

Q1
medium

A jar packed full of marbles can still take in a good amount of dry sand poured over them. Used as a model of matter, this shows that

  1. A matter has nothing separate inside it
  2. B there are spaces between the particles of a substance
  3. C sand is heavier than marbles
  4. D marbles are themselves made of sand
Show answer and explanation

Correct answer: B - there are spaces between the particles of a substance

The sand fills the gaps left between the marbles, just as small particles can occupy the spaces between others. The model says nothing about what marbles are made of, and weight plays no part in it. The model is used precisely because matter does have particles with spaces between them.

Q2
medium

Assertion (A): A spoon of sugar can be stirred into a glass filled to the brim with water without the water spilling over. Reason (R): Water is a liquid and takes the shape of the container it is kept in.

  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: B - Both A and R are true, but R is not the correct explanation of A

Both statements are correct on their own, but they are not connected. The sugar fits in because there are spaces between the water particles, not because water takes the shape of its container. A liquid in a full glass would still spill if the added material had nowhere to go, so R cannot be the explanation of A.

Q3
easy

A few crystals of potassium permanganate are dropped into a jar of still water and left alone. After some hours the whole jar looks purple. This observation supports the idea that

  1. A the crystals grow larger and larger inside water
  2. B matter is made of tiny particles that can spread out on their own
  3. C water is able to make colour by itself
  4. D matter is one continuous piece with nothing separate inside it
Show answer and explanation

Correct answer: B - matter is made of tiny particles that can spread out on their own

The purple colour reaches every part of the jar without any stirring, so something tiny must have moved out of the crystals into all the water. Water cannot create colour, and the crystals actually get smaller as they dissolve, not larger. If matter were one continuous piece, nothing could spread through the water like this.

Q4
hard

Two glasses hold the same amount of water. Plenty of sugar is stirred into the first until no more will dissolve, while only a pinch is stirred into the second. Both look equally clear and colourless. What can we conclude?

  1. A Neither glass has any sugar left in it
  2. B The first glass must look cloudy because it holds more sugar
  3. C How much is dissolved cannot be judged by looking, because dissolved particles are invisible
  4. D The second glass must weigh more than the first
Show answer and explanation

Correct answer: C - How much is dissolved cannot be judged by looking, because dissolved particles are invisible

Dissolved particles are too small to see, so both solutions look alike however much sugar they hold; only tasting or evaporating would tell them apart. A true solution does not turn cloudy. The glass with more sugar dissolved in it is the heavier one, and both clearly still contain sugar.

Q5
medium

Two observations are made with common salt. (i) A spoon of salt stirred into water disappears from sight. (ii) Every sip of that water tastes salty. Together these observations best support the idea that

  1. A water turns salty on its own after standing for a while
  2. B salt sinks to the bottom and stays there as a layer
  3. C salt is made of very tiny particles that spread all through the water
  4. D salt is destroyed as soon as it meets water
Show answer and explanation

Correct answer: C - salt is made of very tiny particles that spread all through the water

The salt is invisible yet its taste is everywhere, so it must have broken up into particles too small to see and spread through the water. It has not been destroyed, because the taste proves it is still present. A layer at the bottom would leave the upper water tasteless, and plain water left standing never becomes salty by itself.

Q6
hard

Equal volumes of water and of a certain other liquid are measured separately and then mixed. The mixture measures a little less than the two volumes added together. The best explanation is that

  1. A particles of one liquid slip into spaces between particles of the other
  2. B the measuring cylinder shrinks when liquids are mixed
  3. C some of the liquid is destroyed during mixing
  4. D the particles of both liquids become smaller on mixing
Show answer and explanation

Correct answer: A - particles of one liquid slip into spaces between particles of the other

A small loss of volume shows that the particles have packed more closely, some of them fitting into gaps that were already present. Matter is not destroyed on mixing, and glass does not shrink. Particles keep their own size; only the spacing between them changes.

Q7
hard

Assertion (A): When a perfume bottle is opened in a still room, a person standing nearby smells it before a person standing far away. Reason (R): Perfume particles travel in straight lines aimed only at the people nearest to the bottle.

  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: C - A is true, but R is false

The assertion is true, because particles need more time to cover a longer distance. The reason is false: perfume particles move in every direction along random zig-zag paths and are not aimed at anybody. So only the assertion stands, and the choices that call A false or accept R are wrong.

Q8
easy

We cannot see the separate particles that make up a piece of chalk because

  1. A they appear only when the chalk is made wet
  2. B they are hidden under a coating of dust
  3. C they keep moving far too fast to be seen
  4. D they are far too small for our eyes to see
Show answer and explanation

Correct answer: D - they are far too small for our eyes to see

The particles of matter are so small that no naked eye can pick them out, so we see only the whole piece of chalk. Speed is not the difficulty, since a still piece of chalk shows no particles either. No coating hides them, and they are present whether the chalk is dry or wet.

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