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

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Consider three liquids: Hydrochloric acid, Sodium hydroxide, and Sugar solution. If tested with a turmeric indicator, which one of the following observations is correct?

Official previous-year question

Verified 1 Aug 2026.

Options

AHydrochloric acid turns the indicator red.
BAll three liquids turn the indicator red with varying intensity.
CSodium hydroxide turns the indicator red.
DSugar solution turns the indicator green.

Did you get this right?

Solution

Correct Option

The correct option is

Sodium hydroxide turns the indicator red.

Explanation

Turmeric is a natural acid-base indicator derived from the Curcuma longa plant. Its active component, curcumin, exhibits specific color changes based on the pH of the medium. It is primarily used to identify basic (alkaline) substances.

Analysis of Liquids

Hydrochloric Acid (Acidic): Turmeric indicator remains yellow in acidic environments. It does not turn red.
Sodium Hydroxide (Basic): Turmeric indicator changes color from yellow to deep red (or reddish-brown) in the presence of bases. This confirms the basic nature of Sodium Hydroxide.
Sugar Solution (Neutral): Turmeric indicator remains yellow in neutral solutions. It shows no color change.

Based on these properties, only Sodium Hydroxide turns the indicator red.

Key Takeaway: Turmeric is a natural indicator that turns red in basic solutions but remains yellow in both acidic and neutral solutions.

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

Sodium hydroxide turns the indicator red.

Explanation

Analysis of Liquids

Hydrochloric Acid (Acidic): Turmeric indicator remains yellow in acidic environments. It does not turn red.
Sodium Hydroxide (Basic): Turmeric indicator changes color from yellow to deep red (or reddish-brown) in the presence of bases. This confirms the basic nature of Sodium Hydroxide.
Sugar Solution (Neutral): Turmeric indicator remains yellow in neutral solutions. It shows no color change.

Based on these properties, only Sodium Hydroxide turns the indicator red.

Key Takeaway: Turmeric is a natural indicator that turns red in basic solutions but remains yellow in both acidic and neutral solutions.