CBSE Class 7 Science Chapter 13 Wastewater Story MCQs with Answers

Waste Water Story is the last chapter of CBSE Class 7 science and include important concepts that are often asked in exams. The Wastewater Story Class 7 Science MCQs are prepared as per the CBSE Class 7 curriculum and the latest 2025-26 syllabus. By solving these Class 7 science MCQs, students will understand the concept easily and get well-prepared for their annual exams.

In this chapter of Class 7 Science Wastewater story students will learn key concepts of the value of clean water and sanitation. The chapter gives an explanation of how wastewater is generated in our homes and environments and how it is treated and then it is discharged back into the environment. Practicing these questions will help to frame answers and remember important points in exam. These MCQ questions will also help in science experiments and practical exam. these shorts points are usually asked in practical exams. So students should seriously learn and practice these Chapter 13 Wastewater Story MCQ Questions for Class 7 Science

Also Check:

• CBSE Class 7 Science MCQs
• CBSE Class 7 English MCQs
• CBSE Class 7 Maths MCQs
• CBSE Class 7 History MCQs

CBSE Class 7 Science Wastewater MCQs for 2025-26

Here is a set of 50 MCQ questions from Class 7 Science Chapter 13 Wastewater Story. These questions cover important topics like the sources of wastewater, sewage treatment processes, the role of microorganisms, and the importance of sanitation and hygiene. By practicing these Class 7 2025 MCQs students can revise key concepts in a simple way and prepare effectively for their annual exams.

Wastewater Story Class 7 MCQs 

1. Wastewater mainly comes from:
   a) Rivers
   b) Homes and industries
   c) Clouds
   d) Plants
   Answer: b) Homes and industries
2. The liquid waste from our houses is called:
   a) Garbage
   b) Sewage
   c) Sludge
   d) Compost
   Answer: b) Sewage
3. Which of the following is NOT a source of wastewater?
   a) Bathing
   b) Cooking
   c) Sleeping
   d) Washing clothes
   Answer: c) Sleeping
4. The network of pipes that carries sewage is known as:
   a) Drainage system
   b) Water supply
   c) Irrigation system
   d) Recycling plant
   Answer: a) Drainage system
5. The solid part separated from sewage during treatment is called:
   a) Sludge
   b) Effluent
   c) Manure
   d) Fertilizer
   Answer: a) Sludge
6. Which harmful substance is often found in industrial wastewater?
   a) Vitamins
   b) Heavy metals
   c) Oxygen
   d) Proteins
   Answer: b) Heavy metals
7. Which microorganism helps in breaking down waste in sewage treatment?
   a) Bacteria
   b) Virus
   c) Fungi
   d) Amoeba
   Answer: a) Bacteria
8. Untreated sewage in water bodies causes:
   a) Clean water
   b) Water pollution
   c) Purification
   d) Desalination
   Answer: b) Water pollution
9. What is the full form of STP?
   a) Sewage Transport Plant
   b) Sewage Treatment Plant
   c) Sludge Transfer Process
   d) Safe Toilet Plan
   Answer: b) Sewage Treatment Plant
10. Which one is an example of organic waste in sewage?
    a) Plastic
    b) Paper
    c) Glass
    d) Iron
    Answer: b) Paper
11. Which gas is often released during sewage treatment?
    a) Oxygen
    b) Methane
    c) Nitrogen
    d) Carbon dioxide
    Answer: b) Methane
12. Which process helps in separating larger objects from sewage water?
    a) Screening
    b) Chlorination
    c) Boiling
    d) Filtration only
    Answer: a) Screening
13. What is the main aim of wastewater treatment?
    a) To make water tasty
    b) To remove harmful substances
    c) To color the water
    d) To freeze the water
    Answer: b) To remove harmful substances
14. Which of these is NOT safe sanitation practice?
    a) Using toilets
    b) Open defecation
    c) Hand washing
    d) Using clean water
    Answer: b) Open defecation
15. Wastewater treatment plants mainly work on:
    a) Physical, chemical, and biological processes
    b) Only physical processes
    c) Only chemical processes
    d) Only biological processes
    Answer: a) Physical, chemical, and biological processes
16. Which one spreads diseases from untreated wastewater?
    a) Sunlight
    b) Insects and flies
    c) Rocks
    d) Sand
    Answer: b) Insects and flies
17. Which of the following can be reused from treated sludge?
    a) Manure
    b) Plastic
    c) Glass
    d) Steel
    Answer: a) Manure
18. Treated water from STPs is often used for:
    a) Drinking directly
    b) Washing and irrigation
    c) Making sweets
    d) None
    Answer: b) Washing and irrigation
19. Which one of these is a natural cleaner of water bodies?
    a) Fish
    b) Bacteria
    c) Plastic
    d) Oil
    Answer: b) Bacteria
20. Which system is more hygienic for disposing of human waste?
    a) Septic tank
    b) Open fields
    c) Rivers
    d) Lakes
    Answer: a) Septic tank
21. Which method is used to kill harmful microbes in treated water?
    a) Screening
    b) Chlorination
    c) Boiling sewage
    d) Freezing sewage
    Answer: b) Chlorination
22. What is the main problem with open drains?
    a) Looks clean
    b) Breeds mosquitoes
    c) Saves money
    d) Is covered properly
    Answer: b) Breeds mosquitoes
23. What type of resource is clean water?
    a) Renewable
    b) Non-renewable
    c) Man-made
    d) Artificial
    Answer: a) Renewable
24. Which of these is a non-biodegradable pollutant in wastewater?
    a) Soap
    b) Plastic
    c) Food waste
    d) Paper
    Answer: b) Plastic
25. What happens when sewage is released into rivers?
    a) Oxygen in water decreases
    b) Fish population increases
    c) Water becomes pure
    d) Water becomes tastier
    Answer: a) Oxygen in water decreases
26. Which one is an eco-friendly sanitation method?
    a) Composting toilets
    b) Open defecation
    c) Dumping in rivers
    d) Throwing waste on roads
    Answer: a) Composting toilets
27. Wastewater treatment reduces the risk of:
    a) Waterborne diseases
    b) Sports injuries
    c) Air accidents
    d) Noise pollution
    Answer: a) Waterborne diseases
28. Which part of sewage is mostly liquid?
    a) Sludge
    b) Effluent
    c) Plastic
    d) Sand
    Answer: b) Effluent
29. Why is water conservation important in wastewater management?
    a) Saves electricity
    b) Reduces the amount of sewage
    c) Produces food
    d) Creates jobs
    Answer: b) Reduces the amount of sewage
30. Which one is NOT a waterborne disease?
    a) Cholera
    b) Typhoid
    c) Malaria
    d) Diarrhea
    Answer: c) Malaria
31. Where should kitchen waste water ideally go?
    a) Open drains
    b) Sewage treatment system
    c) Rivers
    d) Fields
    Answer: b) Sewage treatment system
32. Which solid waste should never be flushed in toilets?
    a) Tissue paper
    b) Plastic bags
    c) Toilet paper
    d) Water
    Answer: b) Plastic bags
33. Sanitation is mainly related to:
    a) Clean surroundings and safe waste disposal
    b) Plant growth
    c) Sports activities
    d) Cooking food
    Answer: a) Clean surroundings and safe waste disposal
34. The first step in a sewage treatment plant is:
    a) Screening
    b) Chlorination
    c) Boiling
    d) Irrigation
    Answer: a) Screening
35. Which method reduces solid organic waste?
    a) Composting
    b) Burning plastic
    c) Throwing in drains
    d) Burying metals
    Answer: a) Composting
36. What is gray water?
    a) Clean water
    b) Wastewater from baths and kitchens
    c) Pure drinking water
    d) Polluted river water
    Answer: b) Wastewater from baths and kitchens
37. Which color is generally associated with safe toilets?
    a) Green
    b) Blue
    c) Yellow
    d) Black
    Answer: b) Blue
38. Which government campaign promotes sanitation in India?
    a) Swachh Bharat Abhiyan
    b) Make in India
    c) Digital India
    d) Skill India
    Answer: a) Swachh Bharat Abhiyan
39. The wastewater from factories is called:
    a) Effluent
    b) Sludge
    c) Drain water
    d) Compost
    Answer: a) Effluent
40. What happens if sewage mixes with drinking water?
    a) Improves health
    b) Causes diseases
    c) Produces oxygen
    d) Purifies water
    Answer: b) Causes diseases
41. Which of these organisms is used in biogas production from sludge?
    a) Anaerobic bacteria
    b) Viruses
    c) Earthworms
    d) Insects
    Answer: a) Anaerobic bacteria
42. Which part of the world still faces open defecation problems?
    a) Some rural areas
    b) All cities
    c) Only deserts
    d) None
    Answer: a) Some rural areas
43. Wastewater management is important mainly to:
    a) Save money
    b) Protect environment and health
    c) Increase exams
    d) Grow taller
    Answer: b) Protect environment and health
44. Which of these is an example of chemical treatment in STPs?
    a) Adding chlorine
    b) Screening
    c) Sedimentation
    d) Composting
    Answer: a) Adding chlorine
45. Which energy can be obtained from sewage treatment?
    a) Biogas
    b) Solar power
    c) Wind energy
    d) Hydropower
    Answer: a) Biogas
46. Which common household product increases water pollution if overused?
    a) Soap and detergents
    b) Salt
    c) Sugar
    d) Rice
    Answer: a) Soap and detergents
47. Wastewater should not be discharged into:
    a) Sewage plant
    b) Rivers and lakes directly
    c) Covered drains
    d) Treatment tanks
    Answer: b) Rivers and lakes directly
48. Which liquid waste is safe for reuse after treatment?
    a) Effluent
    b) Sludge
    c) Sewage
    d) Oil
    Answer: a) Effluent
49. Which simple habit can reduce wastewater at home?
    a) Closing taps when not in use
    b) Keeping taps open
    c) Washing cars with running water
    d) Throwing food in drains
    Answer: a) Closing taps when not in use
50. The final clean water from STPs is called:
    a) Effluent
    b) Sludge
    c) Drainage
    d) Garbage
    Answer: a) Effluent

Chapter-wise CBSE Class 7 Science MCQs with Answers

Very Important Advanced MCQs on Wastewater Story (Class 7 Science)

1. Which step in sewage treatment ensures removal of suspended solids before biological treatment?
   a) Chlorination
   b) Screening and sedimentation
   c) Disinfection
   d) Filtration only
   Answer: b) Screening and sedimentation
2. If untreated sewage enters a river, which immediate change happens first?
   a) Increase in dissolved oxygen
   b) Decrease in dissolved oxygen
   c) Increase in drinking quality
   d) Neutral effect
   Answer: b) Decrease in dissolved oxygen
3. Why does oxygen level drop when sewage is added to rivers?
   a) Oxygen escapes into air
   b) Bacteria consume oxygen while decomposing organic matter
   c) Fish consume more oxygen
   d) Water becomes colder
   Answer: b) Bacteria consume oxygen while decomposing organic matter
4. Which of these best explains why plastic in wastewater is dangerous?
   a) It easily decomposes
   b) It blocks drains and does not biodegrade
   c) It adds nutrients to soil
   d) It helps purify water
   Answer: b) It blocks drains and does not biodegrade
5. Sludge produced in treatment plants is important because:
   a) It pollutes soil
   b) It can be converted into biogas and manure
   c) It makes water tastier
   d) It is easy to dispose of in rivers
   Answer: b) It can be converted into biogas and manure
6. Which method is used in STPs to destroy harmful pathogens in water?
   a) Composting
   b) Chlorination
   c) Sedimentation
   d) Screening
   Answer: b) Chlorination
7. Which statement correctly explains the role of bacteria in wastewater treatment?
   a) They increase bad smell in sewage
   b) They break down organic matter into harmless substances
   c) They convert water into acids
   d) They block pipelines
   Answer: b) They break down organic matter into harmless substances
8. If sewage is left untreated, which of the following diseases is least likely to spread?
   a) Cholera
   b) Typhoid
   c) Tuberculosis
   d) Diarrhea
   Answer: c) Tuberculosis
9. The reason open drains become breeding grounds for mosquitoes is:
   a) Fast flow of water
   b) Stagnant water collected in them
   c) Strong sunlight
   d) Lack of oxygen
   Answer: b) Stagnant water collected in them
10. Which part of sewage treatment produces effluent?
    a) Primary treatment
    b) Secondary treatment
    c) Final treatment
    d) Screening only
    Answer: c) Final treatment
11. Which property of water is mainly affected when sewage is released into it?
    a) Boiling point
    b) Dissolved oxygen level
    c) Color of water permanently
    d) Density
    Answer: b) Dissolved oxygen level
12. If chlorine is not added in the last step of treatment, what risk increases?
    a) Formation of sludge
    b) Survival of harmful microbes
    c) Sedimentation process stopping
    d) Bacteria decomposing waste faster
    Answer: b) Survival of harmful microbes
13. What is the scientific reason why clean toilets improve community health?
    a) They save water
    b) They prevent human waste from mixing with water sources
    c) They improve soil fertility
    d) They produce electricity
    Answer: b) They prevent human waste from mixing with water sources
14. Why is gray water sometimes reused for irrigation?
    a) It contains useful organic matter and is less harmful than black water
    b) It is pure drinking water
    c) It never pollutes soil
    d) It contains heavy metals
    Answer: a) It contains useful organic matter and is less harmful than black water
15. Which part of wastewater management helps recycle nutrients back to the soil?
    a) Effluent
    b) Sludge
    c) Chlorine
    d) Screening
    Answer: b) Sludge
16. The presence of foam in wastewater mostly indicates:
    a) Oil spillage
    b) Detergents and soaps
    c) Plastic waste
    d) Metals
    Answer: b) Detergents and soaps
17. Which chemical used in treatment acts as a disinfectant?
    a) Methane
    b) Chlorine
    c) Oxygen
    d) Hydrogen
    Answer: b) Chlorine
18. Why is biogas from sludge considered renewable?
    a) It is formed from natural gas reserves
    b) It comes from continuously produced organic waste
    c) It cannot be used for energy
    d) It is non-biodegradable
    Answer: b) It comes from continuously produced organic waste
19. If a town does not have a sewage treatment plant, which is the best alternative?
    a) Dumping waste in rivers
    b) Septic tanks and composting toilets
    c) Using more plastic bags
    d) Burning all waste in open air
    Answer: b) Septic tanks and composting toilets
20. The main disadvantage of untreated wastewater in agriculture is:
    a) It adds nutrients
    b) It spreads harmful microbes and chemicals
    c) It increases soil fertility safely
    d) It is odorless
    Answer: b) It spreads harmful microbes and chemicals
21. Which natural process is imitated in sewage treatment?
    a) Evaporation
    b) Decomposition by microorganisms
    c) Photosynthesis
    d) Respiration
    Answer: b) Decomposition by microorganisms
22. Which part of treatment involves sedimentation of heavier particles?
    a) Primary stage
    b) Secondary stage
    c) Tertiary stage
    d) Chlorination
    Answer: a) Primary stage
23. Why is oxygen supplied in aeration tanks during secondary treatment?
    a) To kill bacteria
    b) To help aerobic bacteria decompose organic waste faster
    c) To stop decomposition
    d) To remove heavy metals
    Answer: b) To help aerobic bacteria decompose organic waste faster
24. What is the main limitation of septic tanks in rural areas?
    a) They cannot store any waste
    b) They need cleaning at regular intervals
    c) They work without bacteria
    d) They purify water fully for drinking
    Answer: b) They need cleaning at regular intervals
25. Which correct sequence shows the steps of sewage treatment?
    a) Screening → Sedimentation → Aeration → Disinfection
    b) Disinfection → Screening → Aeration → Sedimentation
    c) Sedimentation → Aeration → Screening → Disinfection
    d) Aeration → Sedimentation → Screening → Disinfection
    Answer: a) Screening → Sedimentation → Aeration → Disinfection

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