Exploring Substances: Acidic, Basic, and Neutral MCQs for UPSC Prelims

116 practice questions covering Exploring Substances: Acidic, Basic, and Neutral, organised into 3 topics. 116 questions include a written explanation. Pick a topic below, or try the samples first.

Practice by topic

acids-bases-and-neutral-substances

26 questions with answers

natural-indicators

26 questions with answers

neutralisation-in-daily-life

25 questions with answers

Sample questions

Q1
easy

Turmeric paper turns red when a drop of

  1. A a basic solution falls on it
  2. B plain distilled water falls on it
  3. C a neutral solution falls on it
  4. D an acidic solution falls on it
Show answer and explanation

Correct answer: A - a basic solution falls on it

Turmeric changes from yellow to red only with a base, which is the whole point of using it as an indicator. An acid leaves turmeric yellow, so the second choice is wrong. A neutral solution and distilled water also leave it yellow, so neither of the last two produces a change.

Q2
medium

Lime water, milk of magnesia and a solution of washing soda are all basic. All three would therefore

  1. A leave both litmus papers unchanged
  2. B turn red litmus paper blue
  3. C turn blue litmus paper red
  4. D taste sour
Show answer and explanation

Correct answer: B - turn red litmus paper blue

Bases turn red litmus blue, so all three would give that change. Turning blue litmus red is what an acid does. Leaving both papers unchanged is the behaviour of a neutral substance. A sour taste belongs to acids, not to these three.

Q3
medium

A few drops of china rose extract are added to a glass of lime water. What colour is expected?

  1. A Yellow
  2. B Orange
  3. C Green
  4. D Magenta
Show answer and explanation

Correct answer: C - Green

Lime water is basic, and china rose extract turns green in a base. Magenta would appear only if the liquid were acidic, which lime water is not. Yellow and orange are not colours this indicator gives with either an acid or a base.

Q4
medium

Statement I: A neutral solution changes the colour of neither litmus paper. Statement II: A neutral solution turns turmeric paper red. Which of these is correct?

  1. A Both statements are correct
  2. B Only Statement II is correct
  3. C Neither statement is correct
  4. D Only Statement I is correct
Show answer and explanation

Correct answer: D - Only Statement I is correct

Statement I is correct, since leaving both litmus papers unchanged is exactly how a neutral solution behaves. Statement II is wrong, because turmeric turns red only with a base and stays yellow in a neutral solution. So only the first statement stands.

Q5
easy

Litmus, the best known laboratory indicator, is obtained from

  1. A lichens
  2. B turmeric roots
  3. C tea leaves
  4. D rose petals
Show answer and explanation

Correct answer: A - lichens

Litmus is a dye taken from lichens, which are small growths found on rocks and tree bark. Rose petals give a different natural indicator, and turmeric roots give the yellow turmeric indicator. Tea leaves are not used to prepare litmus at all.

Q6
medium

Why is it dangerous to taste an unknown liquid in order to find out whether it is acidic?

  1. A It may spoil the taste of the next meal
  2. B It may change colour once it is inside the mouth
  3. C It may be corrosive or poisonous and can injure the mouth and throat
  4. D It may make the liquid useless for the rest of the experiment
Show answer and explanation

Correct answer: C - It may be corrosive or poisonous and can injure the mouth and throat

Laboratory acids and bases can burn the soft lining of the mouth and throat, and some substances are poisonous, so tasting risks serious injury. Spoiling a meal or wasting a sample are trivial worries beside that. Whether the liquid changes colour in the mouth is not the danger, and it would not be safe even if it did not.

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