Class 7 Science Curiosity Chapter 2 Exploring Substances: Acidic, Basic, and Neutral NCERT Solutions

Class 7 Science Curiosity Chapter 2 Exploring Substances: Acidic, Basic, and Neutral NCERT Solutions – are now available for the academic year 2025–26. These solutions provide clear and accurate answers to all the questions and exercises from the Class 7 Science Curiosity textbook, designed to strengthen students’ understanding of key scientific concepts. Written in simple, self-explanatory language, these solutions make learning science engaging and easy to grasp. Whether used for revision, homework, or exam preparation, they serve as a reliable resource for mastering the topic. Students can also download the solutions in PDF format for convenient offline access and an enhanced learning experience.

Class 7 Science Curiosity Chapter 2 Exploring Substances: Acidic, Basic, and Neutral Questions Answers – PDF Download

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1. A solution turns the red litmus paper to blue. Excess addition of which of the following solution would reverse the change?
(i) Lime water
(ii) Baking soda
(iii) Vinegar
(iv) Common salt solution
Answer:
(iii) Vinegar.
Red litmus turning blue indicates that the solution is basic. To reverse this, an acidic solution like vinegar is needed.

2. You are provided with three unknown solutions labelled A, B, and C, but you do not know which of these are acidic, basic, or neutral. Upon adding a few drops of red litmus solution to solution A, it turns blue. When a few drops of turmeric solution are added to solution B, it turns red. Finally, after adding a few drops of red rose extract to solution C, it turns green. Based on the observations, which of the following is the correct sequence for the nature of solutions A, B, and C?
(i) Acidic, acidic, and acidic
(ii) Neutral, basic, and basic
(iii) Basic, basic, and acidic
(iv) Basic, basic, and basic
Answer:
(iv) Basic, basic, and acidic.
Solution A is basic because it turns red litmus paper blue. Solution B is basic because turmeric turns red in a basic solution. Solution C is basic because red rose extract turns green in a basic solution.

3. Observe and analyse Figs. 2.13, 2.14, and 2.15, in which red rose extract paper strips are used. Label the nature of solutions present in each of the containers.

Answer:
Fig. 2.13: Basic solution, as it turns the color of the paper strip to green.
Fig. 2.14: Neutral solution, since there is no change in the color of the paper strip.
Fig. 2.15: Acidic solution, as it turns the color of the paper strip to red.

4. A liquid sample from the laboratory was tested using various indicators:

Based on the tests, identify the acidic or basic nature of the liquid and justify your answer.
Answer:
The liquid sample is acidic because it turned blue litmus red and showed no color change with turmeric—both of which are characteristic properties of acids.

5. Manya is blindfolded. She is given two unknown solutions to test and determine whether they are acidic or basic. Which indicator should Manya use to test the solutions and why?
Answer:
Manya can use olfactory indicators to test whether the solutions are acidic or basic, as these are substances whose odour changes in acidic or basic conditions.

6.  Could you suggest various materials which can be used for writing the message on the white sheet of paper (given at the beginning of the chapter) and what could be in the spray bottle? Make a table of various possible combinations and the colour of the writing obtained.
Answer:

7. Grape juice was mixed with red rose extract; the mixture got a tint of red colour. What will happen if baking soda is added to this mixture? Justify your answer.
Answer:
When baking soda is added to the mixture of grape juice and red rose extract, the red colour will gradually fade. This happens because baking soda is basic in nature and neutralizes the acidity of the grape juice. As the mixture becomes neutral or slightly basic, the red tint disappears.

8. Keerthi wrote a secret message to her grandmother on her birthday using orange juice. Can you assist her grandmother in revealing the message? Which indicator would you use to make it visible?
Answer:
Yes, I can assist her grandmother in revealing the message. Since orange juice is acidic, I would apply red rose extract to the written message, which would make it appear red. This happens because red rose extract turns red in acidic solutions.

9. How can natural indicators be prepared? Explain by giving an example.
Answer:
Natural indicators can be prepared from parts of plants such as flowers, leaves, and vegetables.
Example: Red rose extract preparation
Collect and wash red rose petals, then crush them gently in a glass. Pour hot water over the crushed petals and let the solution sit for 5–10 minutes. Filter out the petals—the coloured liquid is your natural red rose indicator.

10. Three liquids are given to you. One is vinegar, another is a baking soda solution, and the third is a sugar solution. Can you identify them only using turmeric paper? Explain.
Answer:
The liquid that turns turmeric paper red is baking soda, as turmeric turns red in a basic solution. The other two liquids don’t change the color of the turmeric paper, so they are either vinegar or a sugar solution. This is because turmeric stays yellow in acidic or neutral solutions and can’t be used to distinguish them.

11. The extract of red rose turns the liquid X to green. What will the nature of liquid X be? What will happen when excess of amla juice is added to liquid X?
Answer:
Liquid X is basic because it turns red rose extract green. Amla juice is acidic, and when added in excess, it neutralizes the basicity of liquid X, making the solution acidic. The red rose extract will turn this solution red.

12. Observe and analyse the information given in the following flowchart. Complete the missing information.

Answer: