All questions of Matter in Our Surroundings for Class 9 Exam

SI Units of Measurement

SI units are the International System of Units, which is the modern form of the metric system. It is used in scientific and technical fields as a standard system of measurement. The SI system has seven base units, which are used to derive all other units of measurement.

SI Units of Temperature, Pressure, Density and Volume

Temperature: The SI unit of temperature is Kelvin (K), not Celsius (°C).

Pressure: The SI unit of pressure is Pascal (Pa), not atm (atmosphere).

Density: The SI unit of density is kilograms per cubic meter (kg/m3).

Volume: The SI unit of volume is cubic meter (m3). However, liter (L) is also commonly used as a non-SI unit of volume. 1 L = 1000 cm3 = 1 dm3.

Conclusion

Option B is not correct because the SI unit of pressure is Pascal (Pa), not atm (atmosphere). Atm is a non-SI unit of pressure. Therefore, the correct answer is option B.

Incorrect Statement: Matter is continuous in nature.

Explanation:

Matter is made up of small particles called atoms and molecules that have mass and occupy space. These particles are not continuous but are separated by empty spaces. Therefore, the statement that "matter is continuous in nature" is incorrect.

Evidence Supporting the Correct Statements:

a) Matter is made up of particles:

The concept of matter being made up of small particles was first proposed by the Greek philosopher Democritus in the 5th century BC. This idea was later supported by scientists like John Dalton, who proposed the atomic theory of matter in the 19th century. Today, we know that matter is made up of atoms and molecules.

b) Particles of matter are always in a state of motion:

Particles of matter are always in motion, even when they appear to be at rest. This motion can be either random or organized. The kinetic theory of matter explains that the temperature of matter is related to the speed of its particles. When matter is heated, the particles move faster and vice versa.

d) Particles of matter attract each other:

Particles of matter attract each other due to the presence of forces like gravitational, electric, and magnetic forces. These forces allow particles to stick together and form larger structures like molecules, crystals, and even planets.

Conclusion:

In conclusion, the statement that "matter is continuous in nature" is incorrect. Matter is made up of small particles that are separated by empty spaces. These particles are always in motion and attract each other due to the presence of forces.

B) Water is attracted to nonpolar substances, then polar substances, and finally to itself through hydrogen bonding.

The correct answer is option 'C': Evaporation, diffusion, expansion of gases.

Explanation:
When the temperature is increased, several physical processes tend to increase. These processes include evaporation, diffusion, and expansion of gases. Let's understand each of these phenomena in detail:

1. Evaporation:
Evaporation is the process by which a liquid changes into a vapor or gas at temperatures below its boiling point. When the temperature is increased, the kinetic energy of the molecules in the liquid also increases. As a result, more molecules gain enough energy to overcome the attractive forces of the liquid and escape into the gas phase. Therefore, evaporation increases with an increase in temperature.

2. Diffusion:
Diffusion is the process of movement of particles from an area of higher concentration to an area of lower concentration. It occurs due to the random motion of particles. When the temperature is increased, the kinetic energy of the particles also increases. This increased kinetic energy leads to faster and more frequent collisions between particles, resulting in an increased rate of diffusion.

3. Expansion of gases:
When gases are heated, their molecules gain kinetic energy and move faster. This increased molecular motion leads to an increase in the volume of the gas because the molecules now occupy a larger space. Therefore, gases expand when the temperature is raised.

These three phenomena - evaporation, diffusion, and expansion of gases - all increase with an increase in temperature.

Let's summarize the answer:

- Evaporation, the process by which a liquid changes into a vapor or gas, increases with an increase in temperature.
- Diffusion, the movement of particles from an area of higher concentration to an area of lower concentration, increases with an increase in temperature.
- Expansion of gases occurs when the temperature is raised, as the increased kinetic energy of the gas molecules causes them to move faster and occupy a larger volume.

Hence, the correct answer is option 'C': Evaporation, diffusion, expansion of gases.

Understanding States of Matter
Matter exists in different states, primarily solid, liquid, gas, and plasma. Each state has unique characteristics based on the arrangement and movement of its particles.
Characteristics of Gases
- Particle Movement: In gases, particles move freely and rapidly. They do not have a fixed position, allowing them to spread out in any direction.
- Spacing: There is maximum space between gas particles compared to solids and liquids. This spacing allows gases to expand and fill the entire volume of their container.
Comparison with Other States
- Solids: In solids, particles are tightly packed and vibrate in fixed positions. This results in a definite shape and volume.
- Liquids: In liquids, particles are close together but can slide past one another. Liquids have a definite volume but take the shape of their container.
- Plasma: Plasma consists of ionized gases with free-moving charged particles. While particles in plasma can also move freely, they are significantly affected by electric and magnetic fields.
Conclusion
The correct answer is option C: Gas because gases have particles that move freely with a maximum distance between them, allowing for the properties of expansion and compressibility. This unique arrangement makes gases distinct from solids and liquids, which have more structured particle arrangements.

Gas

(b) answer

Sí, the correct answer is C!

Understanding the Statements
Statement A: "Celsius scale is the best scale for measuring temperature."
Statement B: "CO2 (liquid state) is stored under high pressure."
Analysis of Statement A
- The Celsius scale is widely used for everyday temperature measurement, particularly in most countries.
- However, it may not be the best scale for all scientific applications.
- For example, the Kelvin scale is preferred in scientific contexts as it starts from absolute zero, providing a more accurate representation of thermal energy.
Analysis of Statement B
- Carbon dioxide (CO2) in its liquid state must be stored under high pressure.
- This is necessary because CO2 only becomes liquid at pressures above 5.1 atmospheres at room temperature.
- Hence, storing liquid CO2 requires specialized high-pressure containers to maintain its liquid form.
Conclusion
- Statement A is subjective and not universally true; thus, it is not entirely accurate to claim it is the best scale.
- Statement B is a factual statement regarding the storage of liquid CO2 under high pressure.
Final Answer
- Therefore, the correct answer is option 'C': Statement B is true, while Statement A is not necessarily the best.

Latent Heat of Fusion

Latent heat of fusion refers to the amount of heat energy required to change 1 kg of solid into a liquid completely at its melting point. This is a specific type of heat energy that is required for a substance to change phases from a solid to a liquid.

Explanation

When a solid substance is heated, its temperature increases until it reaches its melting point. Once the substance reaches its melting point, the heat energy being added is used to break the bonds between the molecules in the solid, allowing the molecules to move more freely and become a liquid. This process requires a certain amount of heat energy, which is known as the latent heat of fusion.

The latent heat of fusion is a specific amount of heat energy that is required to change 1 kg of a substance from a solid to a liquid at its melting point. It is a characteristic property of each substance and is typically measured in units of J/kg.

For example, the latent heat of fusion of water is 334 kJ/kg. This means that it takes 334 kJ of heat energy to melt 1 kg of ice into liquid water at 0°C.

Conclusion

In conclusion, the latent heat of fusion is the amount of heat energy required to change a substance from a solid to a liquid at its melting point. It is a characteristic property of each substance and is typically measured in units of J/kg.

Understanding the Smell of Food
The rapid detection of food aromas can be attributed to the properties of gases and how they interact with our sensory systems.
High Speed of Gas Particles
- Gases consist of particles that are in constant motion.
- These particles travel at high speeds, allowing them to disperse quickly in the air.
- When food is cooked or heated, volatile compounds are released.
- These compounds are tiny particles that move rapidly, reaching our noses almost instantaneously.
Diffusion of Odors
- The process by which these particles spread out is known as diffusion.
- In the case of gases, diffusion occurs quickly due to the high energy levels of the particles.
- As the food particles collide with air molecules, they disperse throughout the surrounding environment.
Human Sensory Response
- Our olfactory receptors, located in the nasal cavity, are highly sensitive to these odor particles.
- When these particles reach our noses, they bind to the receptors, sending signals to our brain that interpret the smell.
- This system is extremely efficient, enabling us to detect food odors within seconds.
Conclusion
In summary, the reason we can smell food almost instantly is primarily due to the high speed of particles in gases. The rapid motion and diffusion of these tiny particles allow their scent to reach us quickly, stimulating our sense of smell and enhancing our experience of food.

When a solid is heated, its particles absorb energy and start vibrating faster and faster. As the temperature rises, these vibrations become strong enough to overcome the attractive forces holding the particles together.
At the exact temperature where those forces finally break and the solid transforms into a liquid — that magical threshold is called the melting point.

It’s the lowest temperature at which a solid becomes a liquid at normal atmospheric pressure.
Boiling point is for liquid → gas, sublimation is solid → gas, evaporation is slow liquid → gas…
But solid → liquid?
That’s 100% the melting point. 🌡️✨

Yes you are wright c is correct option because liquid and gases particles are many space between them so the have property of fluidity

Understanding Gas Pressure
Gases exert pressure on the walls of their container primarily due to the random movement and collisions of their particles. Here’s a detailed breakdown of why this occurs:
Random Movement of Gas Particles
- Gas particles are in constant, rapid motion.
- They move freely in all directions, resulting in a wide range of velocities.
Collisions with Container Walls
- As gas particles travel, they frequently collide with the walls of their container.
- Each collision exerts a small force on the wall.
Accumulation of Forces
- The total pressure exerted by the gas is the cumulative effect of countless collisions occurring per second.
- The more frequent and forceful these collisions, the higher the pressure exerted on the walls.
Key Factors Influencing Gas Pressure
- Temperature: Higher temperatures increase particle speed, leading to more frequent and forceful collisions.
- Volume: Reducing the volume of the container can increase the rate of collisions, thereby increasing pressure.
- Number of Particles: More particles in a given volume increase the likelihood of collisions, raising the pressure.
Conclusion
In essence, the pressure exerted by gases is a direct result of their dynamic nature and the interactions between the particles and the container walls. Understanding this concept is fundamental in the study of gas behavior and properties.

Understanding Boiling Point
The boiling point of a liquid is a fundamental concept in thermodynamics and chemistry. It refers to the specific temperature at which a liquid transitions into a gas.
Definition of Boiling Point
- The boiling point is defined as the temperature at which the vapor pressure of a liquid equals the atmospheric pressure surrounding it.
- At this temperature, the molecules within the liquid gain enough energy to overcome intermolecular forces, allowing them to escape into the gas phase.
Comparison with Other Points
- Melting Point: This is the temperature at which a solid turns into a liquid. It is different from the boiling point, as it deals with the solid-liquid phase transition.
- Freezing Point: The temperature at which a liquid becomes a solid. Like the melting point, it involves a change of state but in the opposite direction.
- Sublimation Point: This refers to the temperature and pressure at which a solid changes directly into a gas without passing through the liquid state, which is not applicable in the context of liquids boiling.
Importance of Boiling Point
- The boiling point is crucial for various applications, including cooking, industrial processes, and the formulation of chemical substances.
- It also helps in identifying and characterizing substances, as different liquids have distinct boiling points.
In summary, option 'C' is correct because the boiling point specifically refers to the temperature at which a liquid begins to boil and transition into vapor, differentiating it from other thermal transitions such as melting and freezing.

Understanding Gas Compressibility
Gases exhibit a unique property of high compressibility, which sets them apart from solids and liquids. The key reason for this phenomenon lies in the behavior of gas particles.
Random Movement of Particles
- Gases consist of particles (atoms or molecules) that are in constant, random motion.
- This movement is not restricted, allowing particles to spread out and occupy a larger volume.
- The distance between gas particles is significantly greater than in solids and liquids, where particles are more tightly packed.
Low Density
- Because gas particles are spread out, gases have a lower density compared to solids and liquids.
- This low density contributes to the ease with which gases can be compressed.
Interactions Between Particles
- In gases, the forces of attraction between particles are minimal, allowing them to move freely.
- When pressure is applied to a gas, the particles can be pushed closer together, resulting in compression.
Comparison with Solids and Liquids
- Solids have a definite shape and fixed volume due to closely packed particles that vibrate in place.
- Liquids have a fixed volume but take the shape of their container; however, their particles are still closer together than in gases.
- In both solids and liquids, particle movement is restricted, making them less compressible.
Conclusion
In summary, the high compressibility of gases compared to solids and liquids is primarily due to the random movement of particles, which allows them to occupy more space and be compressed easily under pressure. This fundamental characteristic is crucial in various applications, from industrial processes to understanding atmospheric behavior.

Understanding Shape Change Under Force
When evaluating which materials can change their shape under force, it's essential to consider their physical properties and behavior when subjected to stress.
Characteristics of Materials

• Rubber Band:
  - Rubber bands are elastic materials, meaning they can stretch and return to their original shape when the force is removed.
  - This elasticity allows them to deform significantly under tension.
• Piece of Wood:
  - Wood is a rigid material.
  - While it can bend slightly under a significant force, it typically breaks or splinters rather than returning to its original shape.
• Metal Rod:
  - Metal rods are generally strong but also rigid.
  - They can bend under enough force, but like wood, they are likely to remain in that deformed state or fracture if the force exceeds their yield strength.
• Stone:
  - Stone is an extremely rigid material.
  - It does not change shape easily under force and will typically break or shatter instead.

Conclusion
Among the options provided, only the rubber band can change its shape under force and return to its original form once the force is removed. This characteristic is due to its elastic nature, which allows for significant deformation without permanent change. In contrast, the other materials mentioned have rigid structures that resist deformation and do not revert to their original shapes once the force is applied.

Understanding Deposition
Deposition is a fascinating phase transition where a gas transforms directly into a solid without passing through the liquid state. This process is crucial in various natural and industrial phenomena.
Key Characteristics of Deposition:
- Direct Transition: In deposition, gas molecules lose energy and directly condense into a solid form. This bypasses the liquid phase entirely, making it unique among other phase changes.
- Examples in Nature: A common example of deposition is the formation of frost. When water vapor in the air comes into contact with a cold surface, it transforms directly into ice crystals, creating frost without becoming liquid water first.
- Role in Sublimation: Deposition is essentially the reverse of sublimation, where a solid transitions directly into a gas. Together, these processes illustrate the dynamic nature of matter and energy.
Comparison with Other Processes:
- Vaporization: This process involves the conversion of a liquid into a gas, which is the opposite of deposition.
- Sublimation: While sublimation refers to a solid becoming a gas, deposition does the reverse, indicating that they are complementary processes.
- Condensation: This is the transformation of a gas into a liquid, which again is distinct from deposition.
Significance of Deposition:
- Environmental Impact: Deposition plays a vital role in weather patterns and the formation of snowflakes, emphasizing its importance in atmospheric science.
- Industrial Applications: Understanding deposition can aid in processes like freeze-drying and the manufacturing of certain materials where direct solid formation is beneficial.
In summary, deposition is a critical process in both nature and industry, highlighting the intricate behaviors of materials under varying conditions.

Zero on the Celsius scale is the equivalent to 273.15K  . 1- degree rise in Celsius scale is equivalent to the 1- degree rise in the kelvin scale. So , the correct answer is 

Understanding the Three States of Matter
Matter is anything that has mass and occupies space. The three classical states of matter are:
Solid
- Solids have a definite shape and volume.
- The particles in solids are closely packed together, creating a rigid structure.
- They vibrate in place but do not move freely, which gives solids their fixed form.
Liquid
- Liquids have a definite volume but take the shape of their container.
- The particles are less tightly packed than in solids, allowing them to slide past each other.
- This fluidity enables liquids to flow and take the shape of their surroundings.
Gas
- Gases have neither a definite shape nor a fixed volume.
- The particles are far apart and move freely, resulting in gases expanding to fill any available space.
- This characteristic makes gases compressible and easily adjustable to changes in temperature and pressure.
Why Option B is Correct
- Option 'b' (Solid, Liquid, Gas) correctly identifies the three fundamental states of matter.
- While other options may include terms like "Plasma" and "Energy," they do not represent the three primary states of matter.
- Plasma, for example, is a state of matter formed at extremely high temperatures, but it is not one of the classical states typically taught at the basic level.
Conclusion
Understanding these three states is crucial for grasping the behavior of matter in different physical conditions. Each state has unique properties that determine how substances interact in our world.