---
title: "NCERT Solutions for Class 7 Science Chapter 2 Exercise 2.7"
url: https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions/exercise-2-7
dateModified: 2026-10-07T16:06:22+00:00
---

# NCERT Solutions for Class 7 Science Chapter 2 Exercise 2.7

Chapter 2: Exploring Substances: Acidic, Basic, and Neutral. Every question from Exercise 2.7, with full working and the final answer.

Free PDF (16 pages): https://www.swavid.com/api/seo/pdf/ncert/science/class-7/swavid-ncert-solutions-class-7-science-chapter-2-exploring-substances-acidic-basic-and-neutral-13aedb74b7.pdf

## Activity 2.7: Let us experiment

### Question 1

*2 marks · Very short answer*

Do you observe any colour change (Fig. 2.10a)?

**Solution**

1. When a drop of blue litmus solution is added to the diluted lemon juice solution, the colour of the solution turns red.
2. This indicates that lemon juice is acidic in nature, as acids turn blue litmus red.

**Answer:** The blue litmus solution turns red, showing that the lemon juice solution is acidic.

> Common mistake: Stating that blue litmus turns blue instead of red.

### Question 2

*2 marks · Very short answer*

What do you observe? Is there any change in the colour of the solution?

**Solution**

1. As drops of lime water are slowly added and swirled into the test tube, the acidic effect is gradually neutralised.
2. A stage comes when the colour of the solution changes from red back to blue.

**Answer:** The colour of the solution changes from red to blue as lime water is added.

> Common mistake: Failing to mention the transition from red to blue.

### Question 3

*3 marks · Short answer*

Can you predict why there is a change in colour?

**Solution**

1. Initially, the lemon juice solution is acidic and turns the blue litmus red.
2. Lime water is a basic solution which, when added in sufficient quantity, neutralises the effect of the acid.
3. When the acid is completely neutralised, the solution is no longer acidic, causing the colour of the indicator to change from red to blue.

**Answer:** There is a change in colour because lime water (a base) neutralises the acid present in the solution, making it no longer acidic.

> Common mistake: Confusing neutralisation with dilution.

## Related pages

- [All Chapter 2 NCERT solutions](https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions)
- [Exercise 2.1](https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions/exercise-2-1)
- [Exercise 2.2](https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions/exercise-2-2)
- [Exercise 2.4](https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions/exercise-2-4)
- [Exercise 2.5](https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions/exercise-2-5)
- [Exercise 2.6](https://www.swavid.com/science/class/7/chapter/exploring-substances-acidic-basic-and-neutral/ncert-solutions/exercise-2-6)

Solutions written by SwaVid, a personal AI tutor for Class 6 to 10 Maths and Science. Practise this chapter free: https://www.swavid.com/start/student