Topic Details (Notes format)

Atoms and Molecules

Subject: General Science

Book: NCERT Science Class 9

Atoms are the basic units of matter.
- **Laws of Chemical Combination**:
- Law of Conservation of Mass.
- Law of Constant Proportion.
- **Concept of Molecules**:
- Molecules of elements: O₂, N₂.
- Molecules of compounds: H₂O, CO₂.
- **Chemical Formulae**:
- Represent the composition of a compound (H₂O for water).
- **Mole Concept**:
- 1 mole = 6.022 × 10²³ particles.

**Possible Exam Questions:**
1. State the laws of chemical combination.
2. Differentiate between atoms and molecules.
3. What is the significance of a chemical formula?
4. How is the mole concept used in chemistry?
5. Explain Avogadro’s number with an example.

Practice Questions

Which organelle is known as the "powerhouse of the cell"?

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Which organ stores and releases glucose in the human body?

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What is the SI unit of temperature?

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Which gas is most abundant in Earth’s atmosphere?

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What is the main function of the ozone layer?

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What is the chemical formula of water?

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Which component of blood carries oxygen?

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Which element is the most abundant in the Earth’s crust?

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Which gas is released during photosynthesis?

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Which process describes the splitting of a nucleus into smaller nuclei?

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