CBSE Class 9 Science Chapter 1: Matter in our Surroundings NCERT Solutions

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NCERT Solutions PDF Class 9 PDF

CBSE Class 9 Science Chapter 1, "Matter in our Surroundings," introduces the fundamental concept of matter, its various states, and characteristic properties. This chapter's NCERT Solutions offer comprehensive explanations and detailed, step-by-step solutions to all exercises. Students will gain a clear understanding of how to convert temperatures between the Celsius and Kelvin scales. They will also explore the scientific reasons behind common phenomena, such as why naphthalene balls disappear over time and how the scent of perfume spreads through a room, illustrating the concept of diffusion. Furthermore, the solutions help in comparing the forces of attraction between particles in different states of matter. They clarify the physical states of water at different temperatures and provide justifications for why water exists as a liquid and iron as a solid at room temperature. Mastering these concepts is vital for building a strong foundation in physics and chemistry, essential for exam success and a deeper appreciation of the scientific world.

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Quick info

BoardCBSE
ClassClass 9
SubjectScience
Session2026
LanguageEnglish
TypeNCERT Solutions
ChapterChapter 1

Chapter summary

Chapter 1, "Matter in our Surroundings," for Class 9 Science focuses on introducing students to the concept of matter. The NCERT Solutions cover key topics such as the states of matter, temperature conversions between Celsius and Kelvin, the phenomena of sublimation and diffusion, and the forces of attraction between particles. The exercises help students apply these concepts to explain common observations and determine the physical state of substances under different conditions.

Learning outcomes

  • Understand the relationship between Kelvin and Celsius temperature scales.
  • Explain phenomena like sublimation and diffusion with scientific reasoning.
  • Compare the forces of attraction between particles in different states of matter.
  • Determine the physical state of water at given temperatures.
  • Justify the physical state of common substances at room temperature based on their properties.

Topics covered

Paper topics

  • Matter and its states
  • Temperature conversion (Celsius to Kelvin)
  • Temperature conversion (Kelvin to Celsius)
  • Properties of matter
  • Forces of attraction between particles
  • Sublimation
  • Diffusion
  • Physical states of water
  • Characteristics of solids
  • Characteristics of liquids

Important topics

  • States of Matter
  • Temperature Conversions
  • Forces of Attraction between Particles
  • Sublimation and Diffusion
  • Physical State of Water at Different Temperatures

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Questions and Solutions

Question 1

Convert the following temperatures into the Celsius scale:
  1. 300 K
Solution:

To convert a temperature from the Kelvin scale to the Celsius scale, we use the formula: T_{\text{°C}} = T_{\text{K}} - 273

  1. For 300 K:

    T_{\text{°C}} = 300 - 273 = 27

    So, 300 K is equal to 27 °C.
  2. For 573 K:

    T_{\text{°C}} = 573 - 273 = 300

    So, 573 K is equal to 300 °C.

Question 2

Convert the following temperatures into the Kelvin scale:
  1. 25°C
Solution:

To convert a temperature from the Celsius scale to the Kelvin scale, we use the formula: T_{\text{K}} = T_{\text{°C}} + 273

  1. For 25°C:

    T_{\text{K}} = 25 + 273 = 298

    So, 25°C is equal to 298 K.
  2. For 373°C:

    T_{\text{K}} = 373 + 273 = 646

    So, 373°C is equal to 646 K.

Question 3

Give reasons for the following observations:
  1. Naphthalene balls disappear with time without leaving any solid.
  2. We can get the smell of perfume sitting several meters away.
Solution:
  1. Naphthalene balls exhibit the property of sublimation. Sublimation is the process where a solid directly changes into a gas without passing through the liquid state. Due to this property, naphthalene balls gradually vaporize and disappear over time, leaving no solid residue behind.
  2. Perfume consists of volatile substances that vaporize quickly at room temperature. These vapors then spread out and mix with the air particles through a process called diffusion. Because diffusion is a relatively fast process, the scent of the perfume can be detected even from several meters away.

Question 4

Arrange the following in increasing order of the forces of attraction between the particles: water, sugar, oxygen.
Solution:

The forces of attraction between particles are strongest in solids, intermediate in liquids, and weakest in gases.

  • Oxygen is a gas.
  • Water is a liquid.
  • Sugar is a solid.
Therefore, arranging them in increasing order of the forces of attraction between their particles gives: Oxygen < Water < Sugar

Question 5

What is the physical state of water at:
  1. 25°C
  2. 0°C
  3. 100°C?
Solution:

The physical state of water depends on the temperature. Water freezes at 0°C and boils at 100°C at standard atmospheric pressure.

  1. At 25°C, water is in the liquid state. This temperature is above its freezing point and below its boiling point.
  2. At 0°C, water exists in equilibrium between the solid (ice) and liquid states. This is the freezing point of water.
  3. At 100°C, water exists in equilibrium between the liquid and vapour (gas) states. This is the boiling point of water.

Question 6

Give two reasons to justify:
  1. Water at room temperature is a liquid.
  2. An iron almirah is a solid at room temperature.
Solution:
  1. Water is a liquid at room temperature (typically around 25°C) because:
    • It possesses fluidity, meaning it can flow easily.
    • It has a definite volume but takes the shape of its container, indicating it is not rigid.
  2. An iron almirah is a solid at room temperature because:
    • It is rigid and maintains a definite shape, regardless of the container.
    • It has fixed boundaries and does not flow.

Common mistakes

  • Incorrectly applying the conversion formula between Kelvin and Celsius.
  • Confusing the states of matter at specific temperatures, especially at phase transition points.
  • Not clearly articulating the reasons for physical phenomena based on particle behavior.

Revision tips

  • Practice temperature conversion problems thoroughly, ensuring correct formulas are used.
  • Focus on understanding the 'why' behind each observation, linking it to the properties of matter.
  • Review the definitions and examples of sublimation, diffusion, and the forces of attraction between particles.
  • Visualize the states of matter at different temperatures to solidify understanding.

Practice MCQs

Q1. What is the correct formula to convert temperature from Kelvin (K) to Celsius (°C)?

Q2. Which of the following substances has the strongest force of attraction between its particles at room temperature?

Q3. The phenomenon where a substance changes directly from a solid to a gas without passing through the liquid state is called:

Q4. At 0°C, what are the possible physical states of water?

Q5. Why can we smell perfume from several meters away?

Frequently asked questions

What is the main focus of CBSE Class 9 Science Chapter 1?

Chapter 1, "Matter in our Surroundings," focuses on introducing the concept of matter, its different states (solid, liquid, gas), and the properties associated with these states. It also covers temperature conversions and phenomena like diffusion and sublimation.

How do I convert temperature from Kelvin to Celsius using the NCERT Solutions?

To convert from Kelvin to Celsius, you subtract 273 from the temperature in Kelvin. The formula is °C = K - 273. For example, 300 K is 27°C.

How do I convert temperature from Celsius to Kelvin using the NCERT Solutions?

To convert from Celsius to Kelvin, you add 273 to the temperature in Celsius. The formula is K = °C + 273. For example, 25°C is 298 K.

What does it mean for water to be liquid at 25°C and solid/liquid at 0°C?

At 25°C, water is a liquid because this temperature is above its freezing point (0°C) and below its boiling point (100°C). At 0°C, water can exist as both solid (ice) and liquid simultaneously, as it is the freezing point where the phase transition occurs.

What is sublimation and how is it explained in the solutions?

Sublimation is the process where a solid changes directly into a gas without becoming a liquid. The solutions explain this using naphthalene balls, which disappear over time due to sublimation.

How do these NCERT Solutions help in exam preparation?

These solutions provide clear, step-by-step explanations for each question, helping students understand the concepts thoroughly. Practicing these rewritten solutions aids in mastering the chapter's topics and improving problem-solving skills for exams.

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