Chapter 1: The Ever Evolving World of Science.
A. Recalling Ideas
1. Science often begins with:
(a) Difficult theories
(b) Simple questions and playful ideas ✅
(c) Making elaborate notes
(d) Sitting idle
2. Exploration in science is how we approach the unknown with:
(a) Curiosity, questions and an open mind ✅
(b) Confusion and closed mind
(c) Discussion
(d) Confusion and discussion
3. What connects different branches of science like physics, chemistry and biology?
(a) History
(b) Observation and experimentation ✅
(c) Ancient traditions
(d) Games and puzzles
4. Science is a journey of:
(a) Memorising
(b) Learning
(c) Discovery ✅
(d) Revising
5. What is the purpose of a sundial?
(a) To measure weight
(b) To study motion
(c) To tell time using shadows ✅
(d) To generate electricity
6. Which of the following is not a feature of science learning?
(a) Curiosity
(b) Exploration
(c) Passive listening ✅
(d) Hands-on activities
7. Why is asking “why” and “how” important in science?
(a) To impress teachers
(b) To make learning fun
(c) To promote critical thinking ✅
(d) To avoid homework
8. Science helps students solve real-life problems by:
(a) Giving ready-made answers
(b) Helping them memorise all topics
(c) Teaching them how to think and reason ✅
(d) Avoiding practical work
II. Assertion and Reasoning Questions
(a) Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A).
(b) Both Assertion (A) and Reason (R) are true but Reason (R) is not a correct explanation of Assertion (A).
(c) Assertion (A) is true, but Reason (R) is false.
(d) Assertion (A) is false, but Reason (R) is true.
1. Assertion (A): Physics, chemistry, biology and earth science are the branches of science.
Reason (R): These branches are not connected with each other.
Answer: (c) Assertion (A) is true, but Reason (R) is false.
2. Assertion (A): Asking questions, exploring new concepts and carrying out hands-on activities will help you think like a scientist.
Reason (R): Science helps you to approach the unknown with curiosity, questions and an open mind.
Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A).
3. Assertion (A): Our own bodies go through very minor transformations, during adolescence.
Reason (R): Changes occur constantly in nature.
Answer: (d) Assertion (A) is false, but Reason (R) is true.
III. Fill in the blanks
1. The paper plane activity helps us to understand ______ and ______.
Answer: forces and motion
2. Changes like fruit ripening or rusting of iron are ______ changes.
Answer: chemical
3. ______ is the only metal that exists in liquid form at room temperature.
Answer: Mercury
4. Changes in nature are ______.
Answer: constant
5. Exploring ideas requires thoughtful ______.
Answer: explanation
IV. Unjumble the alphabets to get the correct word
1. EEPXORL
Answer: EXPLORE
2. UISCORU
Answer: CURIOUS
3. TINIGNGI
Answer: IGNITING
4. PXEEMRITEN
Answer: EXPERIMENT
V. State whether the following statements are True or False. Correct the false statement.
1. Science is limited to studying the life processes of only plants and animals.
Answer: False
Correction: Science studies all aspects of the natural world.
2. Our own bodies go through very major transformations, during adolescence.
Answer: True
3. Experiments and activities help us to understand science better.
Answer: True
4. Science encourages asking questions and being curious.
Answer: True
5. The Vrihat Samrat Yantra is located in Egypt.
Answer: False
Correction: The Vrihat Samrat Yantra is located in Jaipur, India.
B. Understanding Ideas
1. Give two examples to show that changes are taking place constantly in nature.
Answer: Two examples are -
- Day changes into night
- Growth of plants
2. Why is exploration an important part in learning science?
Answer:
Exploration helps us to understand new ideas by asking questions, observing and experimenting. It develops curiosity and scientific thinking.
3. State the importance of activities and experimentation in science.
Answer:
Activities and experiments help in better understanding, practical learning, and developing problem-solving skills.
4. “Nature has evolved with time.” Justify the statement.
Answer:
Nature is always changing. Living organisms grow, seasons change, and environments transform over time.
5. How does light and shadows help us in exploring and understanding the world around us?
Answer:
Light and shadows help us to understand shapes, movement, and position of objects, and even measure time.
6. Do you agree that science helps to solve the world’s biggest problems? Support your answer with examples from the text.
Answer:
Yes, science helps us to solve major problems like diseases, pollution etc.
For example:
II. Case-based Question
Scientific learning connects different branches like physics, chemistry and biology, helping learners understand the world more completely. It encourages them to see how changes occur, how materials behave, and how life functions. Students who understand science do not just gain knowledge—they learn to solve real-life problems using what they know.
1. How does connecting different branches of science help learners?
Answer:
It helps us to understand the world more completely by connecting ideas from physics, chemistry and biology.
2. What does scientific learning encourage students to observe?
Answer:
It encourages students to observe how changes occur, how materials behave, and how life functions.
3. What is the benefit of understanding science, apart from gaining knowledge?
Answer:
It helps students to solve real-life problems using what they know.
4. Make a scrap book to show 5 different real-life situations in which science has been put to use.
Answer:
- Cooking food
- Using electricity
- Growing plants
- Using medicines
- Transportation
Chapter 2: Exploring Substances: Acidic, Basic and Neutral.
I. Choose the correct option:
1. Products of a neutralisation reaction are always
(a) an acid and a base
(b) an acid and a salt
(c) a salt and water ✅
(d) a salt and a base
2. Turmeric is a natural indicator. On adding its paste to acid and base separately, which colours would be observed?
(a) Yellow in both acid and base
(b) Yellow in acid and red in base ✅
(c) Pink in acid and yellow in base
(d) Red in acid and blue in base
3. A solution changes the colour of turmeric indicator from yellow to red. The solution is
(a) basic ✅
(b) acidic
(c) neutral
(d) either neutral or acidic
4. Which of the following set of substances contain acids?
(a) Grapes, lime water
(b) Vinegar, soap
(c) Curd, milk of magnesia
(d) Curd, vinegar ✅
5. Which of the following is an acid-base indicator?
(a) Vinegar
(b) Lime water
(c) Turmeric ✅
(d) Baking soda
6. Sting of an ant contains
(a) vinegar
(b) common salt
(c) formic acid ✅
(d) baking soda
7. What happens when you add lime water to lemon juice?
(a) Turns blue
(b) Turns red
(c) Turns green
(d) No change ✅
8. What does the hydrangea flower colour depend on?
(a) Age
(b) Soil nature (acidic/basic) ✅
(c) Water
(d) Temperature
9. Which flower helps to detect acids and bases?
(a) Rose ✅
(b) Lily
(c) Sunflower
(d) Jasmine
10. Which indicator changes its smell in acids and bases?
(a) Litmus
(b) Red rose
(c) Onion ✅
(d) Vinegar
II. Assertion and Reasoning Questions
Codes:
(a) Both A and R are true and R explains A
(b) Both A and R are true but R does not explain A
(c) A is true, R is false
(d) A is false, R is true
1. Assertion (A): Acids are sour in taste.
Reason (R): Bases are soapy to touch and bitter in taste.
Answer: (b) Both true, but R is not explanation
2. Assertion (A): Neutralisation reaction is accompanied by evolution of heat.
Reason (R): Neutralisation reaction is a reaction between an acid and a base to form salt and water.
Answer: (a) Both true and R explains A
3. Assertion (A): NaCl (common salt) is a neutral substance.
Reason (R): A solution of NaCl in water turns red litmus blue.
Answer: (c) A is true, R is false
4. Assertion (A): When an ant bites, formic acid is injected in skin.
Reason (R): Applying baking soda on affected part can relieve pain due to neutralisation reaction.
Answer: (a) Both true and R explains A
5. Assertion (A): Both acids and bases change colour of all indicators.
Reason (R): Factory waste is neutralised before disposing in water bodies.
Answer: (d) A is false, R is true
III. Fill in the Blanks
-
Lemon juice and vinegar taste sour because they contain acid.
-
Turmeric and litmus are natural acid-base indicators.
-
Phenolphthalein gives pink colour with lime water.
-
When an acidic solution is mixed with a basic solution, they neutralise each other forming salt and water.
-
An acid and a base neutralise each other, forming salt and water, along with heat.
IV. Match the Following
- 1. Lemon juice → (c) turns red in base
- 2. Litmus → (e) turns red in acid and blue in base
- 3. Neutralisation → (d) reaction between acid and base
- 4. Acid-base indicator → (a) changes colour in presence of acid or base
- 5. Turmeric → (b) natural indicator
V. State whether the following statements are true or false. Correct the false statements.
-
All substances are either acidic or basic.
Answer: False
Correction: Substances can be acidic, basic or neutral. -
Lime water turns red litmus blue.
Answer: True -
Common salt dissolved in water turns blue litmus red.
Answer: False
Correction: Common salt solution is neutral and does not change the colour of litmus. -
Calamine can be used to treat ant’s sting.
Answer: True -
Lemon water is basic in nature.
Answer: False
Correction: Lemon water is acidic in nature.
B. Understanding Ideas
I. Answer the following in one word or one sentence
-
Name a substance that is used to identify whether a given substance is an acid or a base.
Answer: Indicator -
A solution turns red litmus paper blue. What does this indicate about the chemical nature of the solution?
Answer: The solution is basic (alkaline). -
Does a neutralisation reaction always result in the formation of a neutral salt?
Answer: No, it may form acidic or basic salt depending on the strength of acid and base. -
Window cleaners contain ammonia which turns red litmus blue. What is its nature?
Answer: Basic in nature -
Red litmus paper is dipped in a solution; it remains red. What is the nature of the solution?
Answer: Acidic or neutral
II. Answer the following questions
1. Soap solution is taken in a test tube. What is the effect of it on:
(a) Turmeric indicator
Answer: Turns reddish-brown (indicates base)
(b) Rose indicator
Answer: Turns green
(c) Blue litmus
Answer: No change
(d) Red litmus
Answer: Turns blue
2. A doctor advises a patient to take an antacid. How do antacids help in releasing acidity? Explain.
Answer:
Antacids are basic substances. They neutralise excess acid in the stomach through a neutralisation reaction, giving relief from acidity and indigestion.
3. While playing in a park, a child was stung by a wasp. Some elders suggested applying paste of baking soda and others lemon juice as remedy. Which remedy is appropriate and why?
Answer:
A wasp sting is basic in nature, so applying lemon juice (acidic) is appropriate. It neutralises the base and reduces pain.
4. Dorji has unlabeled soft drinks. How will he decide which drink is acidic, basic, or neutral?
Answer:
He can use indicators like litmus paper:
- Acid → turns blue litmus red
- Base → turns red litmus blue
- Neutral → no change
5. Muneesh observed that most of the fish in the pond of her village were gradually dying. She also observed that the waste of a factory in their village is flowing into the pond which probably caused the fish to die.
(a) Explain why the fish were dying.
Answer:
Factory waste made the pond water polluted and either too acidic or basic, harming aquatic life and causing fish to die.
(b) If the factory waste is acidic, how can it be neutralised?
Answer:
By adding a base (like lime or calcium hydroxide) to neutralise the acid.
6. An acidic substance is mixed with an equivalent amount of a base substance. What is the reaction called and what is the product formed?
Answer:
It is called a neutralisation reaction, and the products formed are salt and water.
III. Case-based Questions:
1. The product of neutralisation reaction is always
(a) An acid and a base
(b) An acid and a salt
(c) A salt and water ✅
(d) A salt and a base
2. In neutralisation reaction, heat is
(a) Absorbed
(b) Evolved ✅
(c) Neither absorbed nor evolved
(d) May be evolved or absorbed
3. Why is sodium bicarbonate (eno) used during indigestion?
Answer:
Sodium bicarbonate is basic in nature. It neutralises the excess acid present in the stomach and provides relief from indigestion.
4. After carrying out the neutralisation reaction, the test tube immediately found to be somewhat hot. Explain why.
Answer:
Neutralisation reaction is an exothermic reaction, meaning heat is released during the process. This released heat makes the test tube warm or hot.
C. Analysing, Evaluating and Creating
1. A student says lemon juice and soap water are both neutral. Do you agree or disagree with the statement? Explain giving reasons.
Answer:
I disagree with the statement. Lemon juice is acidic in nature because it contains citric acid. It turns blue litmus red. On the other hand, soap water is basic (alkaline) as it turns red litmus blue and feels slippery. Therefore, both are not neutral; one is acidic and the other is basic.
2. Is it safe to taste a substance to check whether it is acidic or basic? Why or why not?
Answer:
No, it is not safe to taste a substance to check its nature. Some acids and bases can be harmful or corrosive and may cause injury or poisoning. Instead, we should use indicators like litmus, turmeric, or pH paper to test safely.
3. Which substance is more effective in treating a bee sting using vinegar or baking soda? Support your choice with reasoning.
Answer:
A bee sting is acidic in nature. Therefore, baking soda (a base) is more effective. It neutralises the acid from the sting and helps reduce pain and irritation. Vinegar is also acidic, so it would not help in this case.
Chapter 3: Electricity: Circuit And Their Components.
I. Select the Correct Option:
-
Which of the following devices is a source of electrical energy in a circuit?
(a) Switch
(b) Battery ✅
(c) Bulb
(d) Connecting wires -
To connect or disconnect an electric circuit, we should use which component?
(a) Bulb
(b) Battery
(c) LED
(d) Switch ✅ Which of the following is the negative terminal of an electric cell?
(a) A plastic disc
(b) A plastic cap(c) A metal cap
(d) A metal disc ✅
III. Fill in the blanks
-
Electricity flows from the positive terminal to the negative terminal of a cell.
-
A material that allows electric current to pass through it is called a conductor.
-
A continuous and unbroken path for current to flow is called a circuit.
-
The electric bulb glows due to the heating of its filament.
-
Plastic and rubber are examples of insulators.
IV. Match items in Column I with those in Column II
-
Cell → (c) Cell
-
Bulb symbol → (d) Bulb
-
Open switch symbol → (e) Switch
-
Battery symbol → (b) Battery
-
LED symbol → (a) LED
V. State whether the following statements are True or False. Correct the false statement.
-
To make a battery of two cells, the positive terminal of one cell is connected to the negative terminal of the other cell.
True -
Copper and aluminium are insulators.
False
Correct statement: Copper and aluminium are conductors. -
Current can flow through a LED bulb in any direction.
False
Correct statement: Current can flow through an LED bulb in one direction only. -
A circuit with an open switch is called an open circuit.
True -
We use alternating current in devices like remote controls, flashlights and toys.
False
Correct statement: We use direct current (DC) in devices like remote controls, flashlights and toys.
B. Understanding Ideas
I. Answer the following questions in one word or one sentence:
Q1. State the energy transformation taking place in lighting a torch.
Ans: Chemical energy is converted into electrical energy and then into light energy.
Q2. What is the name of the material that allows electricity to pass through them?
Ans: Such materials are called conductors.
Q3. What is the function of a battery in a circuit?
Ans: A battery supplies electrical energy to the circuit.
Q4. What is an electric circuit?
Ans: An electric circuit is a continuous and closed path through which electric current flows.
Q5. Why are electrical wires covered with plastic?
Ans: Electrical wires are covered with plastic because plastic is an insulator and prevents electric shocks.
II. Answer the following question:
Q1. Differentiate between conductors and insulators giving one example of each.
Ans:
| Conductors | Insulators |
|---|---|
| •Conductors allow electric current to pass through them. | •Insulators do not allow electric current to pass through them. |
| •Example: Copper | •Example: Rubber |
Q2. Explain why a bulb does not light up when the circuit is open.
Ans: A bulb does not light up when the circuit is open because the path of electric current is broken. Since current cannot flow through the circuit, the bulb does not glow.
Q3. State four safety rules to follow while using electricity at home.
Ans:
- Never touch electrical switches or appliances with wet hands.
- Do not insert fingers or metal objects into electric sockets.
- Use insulated wires and properly covered plugs.
- Switch off the main power supply before repairing electrical appliances.
Q4. What would happen if we use a wooden stick instead of a metal wire in a circuit? Explain.
Ans:
If we use a wooden stick instead of a metal wire in a circuit, the circuit will not work because wood is an insulator and does not allow electric current to pass through it. Therefore, the bulb or device connected to the circuit will not function.
Q5. How can you test whether a material is a conductor or insulator using a simple electric circuit? Describe the process step by step and list the materials you would use.
Ans:
Materials required:
- One electric cell
- A small bulb
- Connecting wires
- A switch
- Material to be tested
Procedure:
- Make a simple electric circuit using the cell, bulb, switch, and connecting wires.
- Leave a small gap in the circuit.
- Place the material to be tested in the gap.
- Close the switch and observe the bulb.
- If the bulb glows, the material is a conductor.
- If the bulb does not glow, the material is an insulator.
Q6. What are the necessary conditions for electricity to flow through a simple circuit?
Ans:
The necessary conditions for electricity to flow through a simple circuit are:
- The circuit must be complete and closed.
- There must be a source of electrical energy such as a cell or battery.
- Conducting materials should be used for connecting the circuit.
III. Case-based Question
Deepak is visiting his grandparents in a village. Every day, there is a power cut from 8:00 p.m. to 10:00 p.m. His grandparents use a battery-operated emergency light during this time. One evening, the emergency light didn’t work. Deepak opened the light and noticed:
(a) The cells were old and leaking.
(b) The bulb inside was fine.
(c) The switch was working.
(d) He went to the village shop, bought two new cells, inserted them correctly, and the light started working again.
Q1. Why didn’t the emergency light work initially when Deepak switched it on?
Ans:
The emergency light did not work initially because the cells were old and leaking, so they could not supply electrical energy.
Q2. What is the role of cells in a battery-operated device like the emergency light?
Ans:
Cells supply electrical energy to operate the emergency light.
Q3. What will happen if the new cells are inserted in the wrong direction in the emergency light?
Ans:
If the new cells are inserted in the wrong direction, the circuit will not work properly and the emergency light will not glow.
Q4. Which component in the circuit allows or stops the flow of current?
Ans:
The switch is the component that allows or stops the flow of current.
C. Analysing, Evaluating and Creating
Q1. Identify and explain at least ten daily life activities that are affected due to the power cut.
Ans:
-
Lighting: Bulbs and tube lights stop working, making it difficult to see at night.
-
Studying: Students cannot study properly without sufficient light.
-
Cooking: Electric appliances like induction stoves, mixers, and microwaves cannot be used.
-
Using Fans and Air Conditioners: Rooms become hot and uncomfortable without fans or ACs.
-
Mobile Charging: Phones and other electronic devices cannot be charged.
-
Watching Television: TVs and entertainment devices stop working during a power cut.
-
Internet Services: Wi-Fi routers stop working, affecting online classes and communication.
-
Water Supply: Electric water pumps may stop supplying water to homes.
-
Refrigeration: Refrigerators cannot keep food cold for a long time, which may spoil food items.
-
Hospital Equipment: Medical devices that need electricity may stop working if there is no backup power.
-
Lifts and Escalators: Lifts in buildings stop working, causing inconvenience.
-
Business Activities: Shops and offices using computers and machines cannot work properly.
Q2. State the different types of cells used in our daily life and also state in which situation they can be used.
Ans:
| Type of Cell | Uses |
|---|---|
| Dry Cell | Used in torches, remote controls, clocks, and toys. |
| Button Cell | Used in watches, calculators, and hearing aids. |
| Rechargeable Cell | Used in rechargeable torches, cameras, and emergency lights. |
| Lithium-ion Cell | Used in mobile phones, laptops, and tablets. |
| Lead-acid Battery | Used in cars, motorcycles, and inverters. |
| Solar Cell | Used in solar lamps, calculators, and solar panels. |
| Nickel-cadmium Cell | Used in cordless phones and rechargeable devices. |
| Alkaline Cell | Used in cameras, gaming controllers, and flashlights. |
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