Consider the following statements about 'Litmus', a natural indicator: 1. It is extracted from lichens. 2. It has a green colour in distilled water. 3. It turns blue when added to an acidic solution. Which of the statements given above is/are correct?

The correct option is (a). Explanation Litmus is a commonly used natural acid-base indicator. It is a water-soluble mixture of different dyes used to test the acidity or alkalinity of a solution based on colour changes. Statement-wise Analysis - Statement 1 is Correct: Litmus solution is a purple dye extracted from lichens, a plant belonging to the division Thallophyta. It is a symbiotic association between algae and fungi. - Statement 2 is Incorrect: When litmus solution is in a neutral medium, such as distilled water, its natural colour is purple, not green. - Statement 3 is Incorrect: The colour change of litmus depends on the pH of the solution: - An acidic solution turns blue litmus to red. - A basic (alkaline) solution turns red litmus to blue. Key Takeaway Litmus is a natural indicator obtained from lichens. Its neutral colour is purple; it turns red in the presence of acids and blue in the presence of bases.

NCERT Class 7 Science — Chapter 1: Acids, bases and salts

mcqeasy

Consider the following statements about 'Litmus', a natural indicator:

It is extracted from lichens.
It has a green colour in distilled water.
It turns blue when added to an acidic solution.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is (a).

Explanation

Litmus is a commonly used natural acid-base indicator. It is a water-soluble mixture of different dyes used to test the acidity or alkalinity of a solution based on colour changes.

Statement-wise Analysis

Statement 1 is Correct: Litmus solution is a purple dye extracted from lichens, a plant belonging to the division Thallophyta. It is a symbiotic association between algae and fungi.
Statement 2 is Incorrect: When litmus solution is in a neutral medium, such as distilled water, its natural colour is purple, not green.
Statement 3 is Incorrect: The colour change of litmus depends on the pH of the solution:
- An acidic solution turns blue litmus to red.
- A basic (alkaline) solution turns red litmus to blue.

Key Takeaway

Litmus is a natural indicator obtained from lichens. Its neutral colour is purple; it turns red in the presence of acids and blue in the presence of bases.

Your note

More from Chapter 1: Acids, bases and salts

With reference to the chemical nature of substances, consider the following statements: 1. All substances that taste sour contain acids. 2. Substances that taste bitter and feel soapy on touching are generally acidic in nature. 3. Baking soda is an example of a substance that has a bitter taste and is basic in chemical nature. Which of the statements given above is/are correct?

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Which one of the following pairs is correctly matched regarding the acid present in the substance?

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With reference to Turmeric as an indicator, consider the following statements: 1. Turmeric paste remains yellow in acidic solutions. 2. Turmeric paste turns blue in basic solutions. 3. Soap solution applied to a turmeric stain turns it red. Which of the statements given above is/are correct?

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The correct option is (a).

Explanation

Litmus is a commonly used natural acid-base indicator. It is a water-soluble mixture of different dyes used to test the acidity or alkalinity of a solution based on colour changes.

Statement-wise Analysis

Statement 1 is Correct: Litmus solution is a purple dye extracted from lichens, a plant belonging to the division Thallophyta. It is a symbiotic association between algae and fungi.
Statement 2 is Incorrect: When litmus solution is in a neutral medium, such as distilled water, its natural colour is purple, not green.
Statement 3 is Incorrect: The colour change of litmus depends on the pH of the solution:
- An acidic solution turns blue litmus to red.
- A basic (alkaline) solution turns red litmus to blue.

Key Takeaway

Litmus is a natural indicator obtained from lichens. Its neutral colour is purple; it turns red in the presence of acids and blue in the presence of bases.