neutralisation-in-daily-life MCQs for UPSC Prelims

25 practice questions on neutralisation-in-daily-life from the Exploring Substances: Acidic, Basic, and Neutral section of the UPSC Prelims syllabus. 25 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

7 Easy 13 Medium 5 Hard

Sample questions

Q1
medium

Brushing the teeth with toothpaste helps to prevent decay because the paste

  1. A neutralises the acid formed in the mouth
  2. B makes the mouth strongly acidic
  3. C removes all the saliva from the mouth
  4. D adds a thin layer of acid to the teeth
Show answer and explanation

Correct answer: A - neutralises the acid formed in the mouth

Toothpaste is mildly basic, so it cancels the acid produced by bacteria and protects the tooth surface. Adding acid, in any amount, would speed up decay. Making the mouth strongly acidic is the opposite of what is wanted. Saliva itself helps protect the teeth, so removing it would not help.

Q2
easy

The waste liquid from many factories is

  1. A often acidic and harmful to living things
  2. B always pure water
  3. C always neutral and completely safe
  4. D suitable for drinking without treatment
Show answer and explanation

Correct answer: A - often acidic and harmful to living things

Factory waste often carries acids or other harmful substances, which is why it must be treated. It is certainly not pure water, and it is not safe by itself. No untreated factory waste should ever be drunk, so the last choice is dangerous as well as wrong.

Q3
easy

The burning felt after an ant sting is caused by

  1. A the hard outer covering of the ant
  2. B an acidic liquid injected by the ant
  3. C a neutral liquid injected by the ant
  4. D a basic liquid injected by the ant
Show answer and explanation

Correct answer: B - an acidic liquid injected by the ant

An ant injects an acidic liquid, and it is this acid that causes the stinging pain. A basic liquid would not be treated with baking soda, which is itself basic. A neutral liquid would cause no such burning. The ant's outer covering plays no part in the pain.

Q4
medium

Why is lemon juice a poor choice for treating an ant sting?

  1. A It is so strongly basic that it would burn the skin
  2. B It is acidic, and an acid cannot cancel another acid
  3. C It removes the natural colour of the skin
  4. D It is neutral and reacts with nothing at all
Show answer and explanation

Correct answer: B - It is acidic, and an acid cannot cancel another acid

An ant sting is acidic, and only a basic substance can cancel it, so an acidic lemon juice gives no relief. Lemon juice is acidic rather than basic, so the second choice is wrong. It is not neutral, since it clearly turns blue litmus red. Skin colour has nothing to do with the treatment.

Q5
medium

Tooth decay begins when

  1. A bacteria in the mouth act on left-over food and produce acid
  2. B the teeth themselves slowly turn basic
  3. C cold food cools the teeth too quickly
  4. D saliva changes into common salt
Show answer and explanation

Correct answer: A - bacteria in the mouth act on left-over food and produce acid

Bacteria feed on food left between the teeth and produce acid, and that acid attacks the tooth surface. Teeth do not turn basic on their own. Saliva does not turn into salt. Cold food may cause a brief sensitivity, but it is not what starts decay.

Q6
easy

Most toothpastes sold for daily use are

  1. A mildly acidic
  2. B strongly acidic
  3. C mildly basic
  4. D exactly as neutral as pure water
Show answer and explanation

Correct answer: C - mildly basic

Toothpaste is made mildly basic so that it can cancel the acid formed in the mouth. An acidic toothpaste, whether strong or mild, would attack the teeth instead of protecting them. A completely neutral paste would not cancel the acid, so it would give less protection.

Q7
easy

Which household substance is commonly rubbed on an ant sting for relief?

  1. A Vinegar
  2. B Lemon juice
  3. C Tamarind pulp
  4. D A paste of baking soda
Show answer and explanation

Correct answer: D - A paste of baking soda

Baking soda is basic, so it cancels the acid of the sting and eases the burning. Lemon juice, vinegar and tamarind pulp are all acidic, so each would add to the acid already in the skin. None of the last three could bring relief.

Q8
hard

Why must a farmer add the correct amount of the treating material to his soil, and not simply as much as he can?

  1. A Extra material always improves the crop further
  2. B The material becomes harmful only when small amounts are used
  3. C Too much can push the soil to the opposite condition, which also harms the crop
  4. D Soil cannot hold more than a spoonful of any material
Show answer and explanation

Correct answer: C - Too much can push the soil to the opposite condition, which also harms the crop

Adding too much lime can leave soil too basic, and too much manure can leave it too acidic, so either extreme damages the crop. More is not always better, which is why the second choice is wrong. Harm comes from excess, not from small amounts. Soil can clearly hold far more than a spoonful.

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