With reference to the indicator Phenolphthalein, consider the following statements: 1. It is a synthetic indicator. 2. It turns red in an acidic solution. 3. It gives a pink colour in a basic solution. Which of the statements given above is/are correct?

Correct Option The correct option is (c) 1 and 3 only. Explanation Indicators are substances that change colour when added to acidic or basic solutions. They are broadly classified into natural indicators (e.g., litmus, turmeric) and synthetic indicators (e.g., phenolphthalein, methyl orange). Phenolphthalein is a weak acid commonly used in acid-base titrations. Statement-wise Analysis - Statement 1 is Correct: Phenolphthalein is a synthetic indicator. It is chemically synthesized and is not obtained from natural sources like plants (unlike litmus, which is extracted from lichens). - Statement 2 is Incorrect: In an acidic solution, phenolphthalein remains colourless. It does not turn red; red colouration in acidic solutions is characteristic of Methyl Orange. - Statement 3 is Correct: In a basic (alkaline) solution, phenolphthalein turns pink. The intensity of the pink colour can vary depending on the concentration of the base. Key Takeaway Phenolphthalein is a synthetic indicator that is colourless in acidic and neutral media but turns pink in basic media.

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

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With reference to the indicator Phenolphthalein, consider the following statements:

It is a synthetic indicator.
It turns red in an acidic solution.
It gives a pink colour in a basic solution.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

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

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Solution

Correct Option

The correct option is (c) 1 and 3 only.

Explanation

Indicators are substances that change colour when added to acidic or basic solutions. They are broadly classified into natural indicators (e.g., litmus, turmeric) and synthetic indicators (e.g., phenolphthalein, methyl orange). Phenolphthalein is a weak acid commonly used in acid-base titrations.

Statement-wise Analysis

Statement 1 is Correct: Phenolphthalein is a synthetic indicator. It is chemically synthesized and is not obtained from natural sources like plants (unlike litmus, which is extracted from lichens).
Statement 2 is Incorrect: In an acidic solution, phenolphthalein remains colourless. It does not turn red; red colouration in acidic solutions is characteristic of Methyl Orange.
Statement 3 is Correct: In a basic (alkaline) solution, phenolphthalein turns pink. The intensity of the pink colour can vary depending on the concentration of the base.

Key Takeaway

Phenolphthalein is a synthetic indicator that is colourless in acidic and neutral media but turns pink in basic media.

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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Consider the following statements regarding naturally occurring acids: 1. Lactic acid is the primary constituent of vinegar. 2. Oxalic acid is found in spinach. 3. Ascorbic acid is also known as Vitamin C. 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 bases and their sources, consider the following pairs: 1. Calcium hydroxide : Lime water 2. Ammonium hydroxide : Window cleaner 3. Magnesium hydroxide : Soap 4. Sodium hydroxide : Milk of magnesia How many of the above pairs are correctly matched?

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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?

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Correct Option

The correct option is (c) 1 and 3 only.

Explanation

Statement-wise Analysis

Statement 1 is Correct: Phenolphthalein is a synthetic indicator. It is chemically synthesized and is not obtained from natural sources like plants (unlike litmus, which is extracted from lichens).
Statement 2 is Incorrect: In an acidic solution, phenolphthalein remains colourless. It does not turn red; red colouration in acidic solutions is characteristic of Methyl Orange.
Statement 3 is Correct: In a basic (alkaline) solution, phenolphthalein turns pink. The intensity of the pink colour can vary depending on the concentration of the base.

Key Takeaway

Phenolphthalein is a synthetic indicator that is colourless in acidic and neutral media but turns pink in basic media.