NCERT Solutions for Class 7 Science Chapter 13 Question Answers - FREE PDF Download
Our comprehensive guide on NCERT Solutions for Class 7 Science Chapter 13, "Motion and Time," is designed to help students grasp fundamental concepts such as motion, speed, and time. These expertly crafted solutions provide detailed explanations and step-by-step answers to all the textbook questions, ensuring efficient and effective study. This resource is a FREE PDF download and is perfect for reinforcing classroom learning and offering additional practice. Master Chapter 13 with ease using our NCERT solutions.
Table of Content
Aligned with the latest Class 7 Science syllabus, the Class 7 Science chapter 13 question answers offer clear explanations that break down complex ideas and empower true learning. Don't settle for memorisation – download your FREE PDF today, boost your exam confidence, and become a champion in this chapter!
1. Fill in the blanks:
a. Cleaning of water is process of removing ________.
Ans: Cleaning of water is process of removing contaminants.
b. Wastewater released by houses is called ________.
Ans: Wastewater released by houses is called sewage.
c. Dried ________ is used as manure.
Ans: Dried dung is used as manure.
d. Drains get blocked by ________ and ________.
Ans: Drains get blocked by plastic and sludge.
2. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas.
Ans: Sewage is a kind of used water or wastewater that has been emitted by houses, industries, hospitals, offices, and other users. It also features subsurface storage for rainfall. It may contain dangerous chemicals and organisms that can endanger human life.
Algae can quickly develop when given various nutrients, resulting in a decreased amount of dissolved oxygen in the water. This is why sewage should not be discharged into seas and rivers.
3. Why should oils and fats be not released in the drain? Explain.
Ans: Oil and fats should not be poured down the drain since they are not dissolved in water and float on top of it. It can clog drains and, if released into bodies of water, can harm aquatic life.
4. Describe the steps involved in getting clarified water from wastewater.
Ans: Wastewater treatment has physical, chemical, and biological processes.
a. Waste water is filtered using bar screens to eliminate large materials such as rags, twigs, cans, plastic packets, napkins, and so on.
b. Water is routed through a grit and sand removal tank, allowing sand, grit, and pebbles to settle.
c. The water is then allowed to settle in a big settling tank, where solid feces known as sludge is removed using a scarper.
d. Air is poured into the clarified water to assist aerobic bacteria in growing and consuming wastes.
e. Water of this kind is dumped into rivers or ponds.
5. What is sludge? Explain how it is treated.
Ans: Sludge is a solid waste material that settles in secondary water treatment. Generally, it is scraped out from the bottom. The clarified water is then discharged. Sludge is stored in a separate tank and treated with anaerobic bacteria, which creates biomass that can be used as bio manure.
6. Untreated human excreta is a health hazard. Explain.
Ans: Millions of bacteria live in the human stomach and expel with the feces. If human excreta is dumped directly into the soil or water, it can pollute both the water and the soil. Under favorable conditions, the bacteria divide and multiply, and when the water reaches the earth table, it might affect a bigger population that consumes it. It can induce water-borne diseases such as typhoid and cholera.
7. Name two chemicals used to disinfect water.
Ans: Water disinfection involves removing or deactivating pathogenic bacteria, as well as killing them. Microorganisms are rendered inactive, putting an end to their development and reproduction. If germs are not removed from drinking water, humans will develop unwell from drinking water. Chlorine and ozone are the two chemicals used in water disinfection.
8. Explain the function of bar screens in a wastewater treatment plant.
Ans: When waste water is pumped through bar screens, it serves as a large screen. In the first step of cleaning water, large materials such as rags, twigs, cans, plastics, and napkins are removed.
9. Explain the relationship between sanitation and disease.
Ans: Sanitation is a public health issue. Sanitation includes the prevention of disease, the provision of safe drinking water, and the proper disposal of garbage. Diseases are spread when cleanliness standards are not met. Dirty water serves as a breeding ground for mosquitoes that transmit diseases. Improper sewage disposal can result in water-borne sickness. As a result, sanitation is the utmost pathogen rescue and can result in a disease-free environment.
10. Outline your role as an active citizen in relation to sanitation.
Ans: All humans have a responsibility to play in keeping our environment clean as engaged and knowledgeable citizens. We can begin from home. Adopting excellent sanitation techniques should be a way of life for all of us. Our energy, ideas, and excitement can have an impact on others. And encourage people to maintain a healthy living environment for the benefit of society.
11. Here is a crossword puzzle: Good luck!
Across
3. Liquid waste products.
4. Solid waste extracted in sewage treatment.
6. A word related to hygiene
8. Waste matter discharged from the human body.
Down
1. Used water.
2. A pipe carrying sewage.
3. Micro-organisms which cause cholera.
7. A chemical to disinfect water.
Ans: Across:
3. Liquid waste product- Sewage
4. Solid waste extracted in sewage treatment- Sludge
6. A word related to hygiene- Sanitation
8. Waste matter discharged from human body- Excreta
Down: 1. Used water- wastewater
2. A pipe carrying sewage- Sewer
5. Microorganisms which causes cholera- Bacteria
7. A chemical to disinfect water- Ozone
12. Study the following statements about ozone:
a. It is essential for the breathing of living organisms.
b. It is used to disinfect water.
c. It absorbs ultraviolet rays.
d. Its proportion in the air is about 3%.
Which of these statements are correct?
i. a., b. and c.
ii. b. and c.
iii. a. and d.
iv. All four
Ans: ii.
Explanation: Ozone, often known as trioxygen, is an inorganic molecule having the formula $\mathrm{O}_{3}$. It's a pale blue gas with a pronounced unpleasant odor. Oxygen is required for living beings to breathe. As a result, statement a. is incorrect
Ozone is a powerful oxidant, even more potent than chlorine. Ozone is used in water to disinfect, deodorize, decolorize, and degrade organic compounds. As a result, statement b. is correct.
The ozone layer, also known as the ozone shield, is an area of the earth's stratosphere that absorbs the majority of the sun's UV radiation. As a result, statement c. is correct.
The concentration of ozone in the atmosphere is $0.000004 \%$. As a result statement d. is incorrect.
Therefore, the correct answer is (ii).
Topics Covered in Class 7 Science Chapter 13 Wastewater Story
Benefits of Wastewater Story Class 7 Solutions
NCERT Solutions of Wastewater Story class 7 is an easy and scoring chapter offering elementary knowledge and a comprehensive brief.
Class 7 science wastewater story questions answers understandably and help students comprehend the chapter and the chapter's contents and answer questions efficiently.
NCERT Solutions for class 7 Science chapter 13 states the importance of Water in every individual's life.
The chapter Wastewater Story class 7 briefly explains the transition of clean water into dirty water and the measures that need to be implemented to reuse and recycle Wastewater.
NCERT class 7 science wastewater story question answers focus on contaminating issues with natural resource water and its dire consequences.
The wastewater story class 7 questions with answers provide an updated syllabus, learning provisions, and revision materials to keep students hassle-free for the rest of the year.
NCERT Solutions for wastewater story class 7 solutions contain all the important topics and concepts under Wastewater Story.
Students can save much time referring to the wastewater management class 7 questions and answers during a test or an exam.
The mock exercises, activities, and the list of questions given at the end of the science chapter 13 class 7 question answers create extensive comprehension of all the crucial topics highlighted in the chapter.
Important Study Material Links for Class 7 Science Chapter 13
Conclusion
NCERT Solutions plays a crucial role in wastewater story class 7 exam preparation. Start by thoroughly reading the textbook chapter. After that, solve the class 7 science chapter 13 question answers. You can find detailed solutions on Vedantu that align with CBSE guidelines. Download the free NCERT Solutions for class 7 Science Chapter 13 Wastewater Story to guide your exam preparation with expert-reviewed answers.
NCERT Solutions for Class 7 Science - Other Chapter-wise Links for FREE PDF
Dive into our FREE PDF links offering other chapter-wise NCERT solutions prepared by Vedantu Experts to help you understand and master fundamental scientific concepts.
Related Study Material Class 7 Science
FAQs on NCERT Solutions for Class 7 Science Chapter 13 Wastewater Story
1. What is the correct solution for the crossword puzzle in NCERT Class 7 Science Chapter 13?
The NCERT solutions provide the correct answers for the crossword puzzle based on the chapter's key terms. The solutions are:
- Across: 3. Sewage, 4. Sludge, 6. Sanitation, 8. Excreta.
- Down: 1. Wastewater, 2. Sewer, 5. Bacteria, 7. Ozone.
2. How do the NCERT solutions explain the harmful effects of discharging untreated sewage?
The NCERT solutions for Chapter 13 explain that untreated sewage is harmful because it contains dangerous chemicals and disease-causing organisms. When discharged into rivers or seas, the nutrients in the sewage can cause excessive algal growth (eutrophication). This depletes the dissolved oxygen in the water, which can kill fish and other aquatic life, severely damaging the ecosystem.
3. According to the NCERT textbook, why should oils and fats not be released into drains?
The NCERT solutions clarify that oils and fats should not be poured down the drain because they are not soluble in water. They harden and accumulate inside pipes, causing severe blockages. If they reach a water body, they form a layer on the surface, which prevents oxygen from dissolving into the water and harms aquatic organisms.
4. What are the key steps to get clarified water from wastewater, as explained in the Chapter 13 solutions?
The NCERT solutions for "Wastewater Story" outline a multi-step process for wastewater treatment to get clarified water:
- Physical Filtration: Wastewater is first passed through bar screens to remove large objects like rags, plastics, and cans.
- Grit and Sand Removal: The water then flows into a tank where the speed is reduced to allow sand, grit, and pebbles to settle down.
- Sedimentation: In a large settling tank, solid waste like faeces, called sludge, settles at the bottom and is removed with a scraper. Floatable materials like oil and grease are removed with a skimmer. The water at this stage is called clarified water.
5. How can students access the complete NCERT Solutions for Class 7 Science Chapter 13 for the 2025-26 session?
Students can find detailed, step-by-step NCERT Solutions for Class 7 Science Chapter 13, "Wastewater Story," on the Vedantu website. These solutions are prepared by subject matter experts and are fully aligned with the latest CBSE 2025-26 syllabus, helping you understand the correct methods to answer all textbook questions.
6. Why is untreated human excreta considered a major health hazard in the NCERT solutions?
The NCERT solutions explain that untreated human excreta is a significant health hazard because it contains millions of harmful microorganisms, including bacteria and viruses. When this waste contaminates soil or water sources (like groundwater), it can spread serious water-borne diseases such as cholera, typhoid, and dysentery to a large population that may consume the contaminated water.
7. What is the scientific reason for using chemicals like chlorine and ozone to disinfect water, as mentioned in the NCERT solutions?
The NCERT solutions identify chlorine and ozone as key disinfectants. The scientific reason they are used is that they are powerful oxidising agents. They effectively kill or inactivate harmful pathogenic microorganisms (like bacteria and viruses) present in the water by destroying their cell walls or disrupting their reproductive processes. This makes the water safe for human consumption and prevents the spread of disease.
8. Beyond just filtering, what is the specific function of bar screens in the initial stage of a wastewater treatment plant as per the NCERT solutions?
According to the NCERT solutions, the specific function of bar screens is not just general filtration but the crucial first step of primary treatment. They are designed to remove large, solid objects such as rags, sticks, plastic bags, and cans from the incoming wastewater. This is essential to prevent damage and clogging of the pumps and other equipment in the later stages of the treatment plant.
9. How do the NCERT solutions for Chapter 13 help students understand their role as active citizens in promoting sanitation?
The NCERT solutions for this chapter encourage students to become active citizens by highlighting their responsibilities. They explain that students can contribute by:
- Not throwing waste, oils, or chemicals down the drain.
- Ensuring their home and school sanitation systems work correctly.
- Spreading awareness about the importance of clean water and proper waste disposal.
- Reporting any open drains or leaking sewer lines to the local authorities.
This helps connect textbook knowledge to practical, responsible actions.
10. What is the difference between sludge and sewage, and how are they treated differently in a wastewater treatment plant?
The NCERT solutions clarify the key differences between these two terms:
- Sewage is the total liquid wastewater released from homes, industries, and hospitals. It is the incoming raw material for the treatment plant.
- Sludge is the semi-solid residue that settles at the bottom of sedimentation tanks after primary and secondary treatment of sewage.
Their treatment methods are also different. Sewage undergoes the full treatment process (screening, settling, aeration), while the collected sludge is transferred to a separate tank called a digester. Here, anaerobic bacteria decompose it, producing useful biogas and nutrient-rich manure.
