NCERT Solutions for Class 9 Science Chapter 1 – Matter in Our Surroundings

इस अध्याय में हम जानेंगे कि “पदार्थ” क्या होता है, उसके कणों की विशेषताएँ क्या हैं, और कैसे पदार्थ विभिन्न अवस्थाओं में पाया जाता है — ठोस, द्रव और गैस। इसमें गुण, व्यवहार, तापमान, दाब और अंतरकणीय आकर्षण जैसे महत्वपूर्ण सिद्धांतों को सरल भाषा में समझाया गया है। यह अध्याय विज्ञान की नींव को मजबूत करता है और रोज़मर्रा की चीज़ों को वैज्ञानिक दृष्टिकोण से देखने की प्रेरणा देता है।

Question 1: Which of the following are matter?

Answer: Chair, air, almonds, cold-drink, smell of perfume are matter. Love, hate, thought, smell (as sensation), cold (as feeling) are not matter.

Question 2: Why does the smell of hot sizzling food reach you from a distance, but cold food doesn’t?

Answer: Hot food releases vapors that diffuse faster due to higher kinetic energy. Cold food diffuses slowly, so you need to be closer to smell it.

Question 3: A diver cuts through water in a pool. What property of matter does this show?

Answer: This shows that particles of matter have space between them, allowing movement — called interparticle space.

Question 4: What are the characteristics of particles of matter?

Answer:

• Particles have space between them.
• They are constantly moving.
• They attract each other.
• They are very small and invisible to the naked eye.

Question 5: Arrange the following in increasing order of density:

Answer: Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron

Question 6(a): Tabulate the differences in the characteristics of states of matter.

Question 6(b): Comment upon the following:

• Rigidity: Property of solids to retain shape.
• Compressibility: Gases are highly compressible; solids are least.
• Fluidity: Liquids and gases can flow.
• Filling a gas container: Gases fill the entire container.
• Shape: Solids have fixed shape; liquids and gases don’t.
• Kinetic Energy: Highest in gases, lowest in solids.
• Density: Highest in solids, lowest in gases.

Question 7: Give reasons

(a) A gas fills completely the vessel in which it is kept.

👉 Because gas particles move freely and randomly in all directions.

(b) A gas exerts pressure on the walls of the container.

👉 Due to constant collisions of gas particles with container walls.

(c) A wooden table should be called a solid.

👉 It has definite shape, volume, and rigidity.

(d) We can easily move our hand in air but not through a solid block of wood.

👉 Because particles in solids are tightly packed, unlike gases.

Question 8: Why does ice float on water?

Answer: Ice has lower density than water due to its open cage-like structure formed by hydrogen bonding.

Question 9: Convert the following temperature to Celsius scale:

(a) 300 K → 27°C (b) 573 K → 300°C

Question 10: What is the physical state of water at:

(a) 250°C → Gas (steam) (b) 100°C → Liquid and gas (boiling point)

Question 11: Why does temperature remain constant during change of state?

Answer: Because heat energy is used to break intermolecular forces, not to increase temperature.

Question 12: Suggest a method to liquefy atmospheric gases.

Answer: By applying high pressure and reducing temperature.

Question 13: Why does a desert cooler cool better on a hot dry day?

Answer: Because dry air increases evaporation rate, which absorbs heat and cools the air.

Question 14: How does water in an earthen pot become cool?

Answer: Water seeps through pores and evaporates, taking away heat and cooling the remaining water.

Question 15: Why does our palm feel cold when we put acetone/petrol/perfume on it?

Answer: These liquids evaporate quickly, absorbing heat from the skin and making it feel cold.

Question 16: Why can we sip hot tea faster from a saucer than a cup?

Answer: Saucer has larger surface area, increasing evaporation and cooling the tea faster.

Question 17: What type of clothes should we wear in summer?

Answer: Light-colored, cotton clothes — they absorb sweat and allow evaporation, keeping us cool.

Question 18: Convert the following temperatures to Celsius scale:

(a) 293 K → 20°C (b) 470 K → 197°C

Question 19: Convert the following temperatures to Kelvin scale:

(a) 25°C → 298 K (b) 373°C → 646 K

Question 20: Give reasons

(a) Naphthalene balls disappear over time without leaving solid.

👉 They undergo sublimation — solid to gas directly.

(b) We can smell perfume from a distance.

👉 Perfume vapors diffuse in air and reach our nose.

Question 21: Arrange in increasing order of forces of attraction:

Answer: Oxygen < Water < Sugar

Question 22: Physical state of water at—

(a) 25°C → Liquid (b) 0°C → Solid and liquid (melting point) (c) 100°C → Liquid and gas (boiling point)

Question 23: Justify

(a) Water at room temperature is a liquid.

👉 It has no fixed shape but definite volume and flows easily.

(b) Iron almirah is a solid at room temperature.

👉 It has fixed shape, volume, and rigidity.

Question 24: Why is ice at 273 K more effective in cooling than water at same temperature?

Answer: Ice absorbs latent heat during melting, providing extra cooling.

Question 25: What produces more severe burns — boiling water or steam?

Answer: Steam, because it carries latent heat of vaporization.

Question 26: Name A, B, C, D, E and F in the diagram showing change of state.

Answer:

• A: Melting (Solid → Liquid)
• B: Vaporization (Liquid → Gas)
• C: Condensation (Gas → Liquid)
• D: Freezing (Liquid → Solid)
• E: Sublimation (Solid → Gas)
• F: Deposition (Gas → Solid)

अक्सर पूछे जाने वाले प्रश्न (FAQs)

Q1. क्या गंध भी पदार्थ होती है?

👉 अगर वह किसी भौतिक वस्तु से निकल रही हो (जैसे इत्र की गंध), तो वह वाष्प के रूप में पदार्थ मानी जाती है।

Q2. पदार्थ के कणों में गति क्यों होती है?

👉 क्योंकि उनमें ऊर्जा होती है, जिससे वे निरंतर गतिशील रहते हैं।

Q3. क्या ठोस पदार्थ भी फैल सकते हैं?

👉 बहुत कम मात्रा में, लेकिन हाँ — जैसे धातु की छड़ गर्म होने पर फैलती है।

Q4. वाष्पीकरण से ठंडक कैसे मिलती है?

👉 वाष्पीकरण के दौरान ऊष्मा का अवशोषण होता है, जिससे आसपास का तापमान कम हो जाता है।

Q5. क्या सभी गैसें एक ही तरह से व्यवहार करती हैं?

👉 नहीं, उनके अणुओं का आकार, द्रव्यमान और आकर्षण बल अलग-अलग होते हैं।

निष्कर्ष | NCERT Solutions for Class 9 Science Chapter 1 – Matter in Our Surroundings

Matter in Our Surroundings अध्याय हमें यह समझाता है कि पदार्थ केवल ठोस या तरल नहीं होते — वे ऊर्जा, गति और आकर्षण के नियमों से संचालित होते हैं। यह अध्याय विज्ञान की सोच को विकसित करता है और छात्रों को रोज़मर्रा की घटनाओं को वैज्ञानिक दृष्टिकोण से देखने की प्रेरणा देता है।