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Do You Know
Q1. Process without a Chemical Reaction – Melting of Wax
A chemical reaction involves the formation of a new substance with different properties. However, melting of candle wax is a physical change, not a chemical one.
Why melting is not a chemical reaction:
- Only the state changes (solid → liquid)
- No new substance is formed
- It is reversible (wax solidifies again on cooling)
Other options involve chemical reactions:
- Digestion → food breaks into simpler substances
- Respiration → glucose reacts with oxygen to release energy
- Burning of wax → produces new substances like carbon dioxide and water
Conclusion: Melting of wax is a physical change, so no chemical reaction occurs.
Q2. Image by Plane Mirror – Virtual and Erect
A plane mirror always forms an image that is virtual (not real) and erect (upright).
Key properties of the image:
- Virtual → cannot be formed on a screen
- Erect → straight, not upside down
- Same size as the object
- Laterally inverted (left-right reversed)
- Equal distance behind the mirror as the object is in front
Why virtual?
Light rays only appear to come from behind the mirror; they do not actually meet.
Example: Your reflection in a mirror.
Q3. Amphoteric Oxide – Aluminium Oxide (Al₂O₃)
Amphoteric oxides are substances that can react with both acids and bases.
Why Al₂O₃ is amphoteric:
- Reacts with acids → forms salt and water
- Reacts with bases → also forms salt and water
Other options:
- Na₂O, MgO, K₂O → basic oxides (react only with acids)
Example reactions:
- With acid: Al₂O₃ + Acid → Salt + Water
- With base: Al₂O₃ + Base → Salt + Water
Conclusion: Aluminium oxide shows dual behavior, so it is amphoteric.
Q4. Requirements for Autotrophic Nutrition
Autotrophic nutrition (like in green plants) is the process of making food using photosynthesis.
All required components:
- Carbon dioxide (from air)
- Water (from soil)
- Sunlight (energy source)
- Chlorophyll (green pigment to trap light)
Process summary:
Plants use sunlight energy to convert carbon dioxide and water into glucose (food) and oxygen.
Equation (simple form):
CO₂ + H₂O → Glucose + O₂ (in presence of sunlight & chlorophyll)
Conclusion: All given factors are necessary, so the correct answer is “All of the above.”
Q5. Control of Life Processes – Nervous & Endocrine Systems
In humans, life processes are controlled and regulated by two main systems:
1. Nervous System
- Works through electrical signals
- Fast response
- Controls actions like movement, thinking, reflexes
2. Endocrine System
- Works through hormones
- Slower but long-lasting effects
- Controls growth, metabolism, reproduction
How they work together:
- Nervous system gives quick responses
- Endocrine system maintains long-term balance
Example:
- Fear → nervous system reacts instantly
- Growth → controlled by hormones over time
Conclusion: Both systems coordinate to control body functions.