All questions of Particulate Nature of Matter for Class 8 Exam

Understanding Boiling
When a liquid reaches its boiling point, it undergoes a specific physical process that transforms it into vapor. This process is known as boiling.
What is Boiling?
- Boiling occurs when a liquid's temperature rises to its boiling point, where the vapor pressure equals the atmospheric pressure.
- At this point, bubbles form within the liquid and rise to the surface, releasing vapor into the air.
Key Characteristics of Boiling
- Temperature Specific: Every liquid has a unique boiling point, which is influenced by atmospheric pressure.
- Rapid Process: Unlike evaporation, which can occur at any temperature and happens slowly, boiling happens rapidly when the boiling point is reached.
Comparison with Other Processes
- Sublimation: This is when a solid turns directly into vapor without passing through a liquid state, e.g., dry ice.
- Evaporation: This occurs at any temperature and involves molecules at the surface of a liquid escaping into the vapor phase.
- Condensation: This is the opposite of boiling, where vapor turns back into a liquid, usually when the temperature drops.
Conclusion
In summary, boiling is a specific type of phase transition from liquid to vapor that occurs at a defined temperature known as the boiling point. It is a critical concept in understanding the behavior of liquids under heat and pressure.

Interparticle Attractions in Gases
In gases, the interparticle attractions are characterized by their minimal nature. Understanding these attractions helps explain the behavior of gases in various conditions.
Nature of Interparticle Attractions
- Almost Negligible: In gases, the forces of attraction between particles are extremely weak. This is due to the large distances between gas particles, allowing them to move freely and independently.
- Kinetic Energy Dominance: The kinetic energy of gas particles is much higher compared to the attractive forces. This high kinetic energy results in rapid movement, further minimizing the effect of any attractions.
Comparison with Liquids and Solids
- Weaker than in Liquids: In liquids, particles are closer together, and intermolecular forces are stronger, allowing for a more structured arrangement. Gases, on the other hand, have negligible attraction, making them more compressible and less dense.
- Not Equal to Solids: In solids, particles are tightly packed and held together by strong forces of attraction, resulting in a fixed shape. This is in stark contrast to gases, where the particles are far apart and can fill any available space.
Summary
- The interparticle attractions in gases are almost negligible.
- The high kinetic energy of gas particles overcomes any potential attractions.
- This characteristic allows gases to expand, compress, and flow easily.
Understanding these concepts is crucial for grasping the behavior of gases in various scientific applications and everyday phenomena.

Understanding Evaporation and Boiling
Evaporation and boiling are both processes that involve the transition of a liquid into a gas, but they occur under different conditions and mechanisms. Here's a detailed explanation of what sets them apart.
Evaporation
- Occurs at the Surface: Evaporation happens only at the surface of the liquid. Molecules at the surface gain enough energy to break free from the liquid and enter the gas phase.
- Can Occur at Any Temperature: This process can take place at any temperature, even below the boiling point of the liquid. For example, water can evaporate at room temperature.
- Dependence on Surface Area: The rate of evaporation increases with a larger surface area, as more molecules are exposed to the air.
Boiling
- Occurs Throughout the Liquid: Boiling is a rapid process that occurs throughout the entire volume of the liquid, not just at the surface. Bubbles form within the liquid as vapor pressure builds up.
- Requires a Specific Temperature: Boiling occurs at a specific temperature called the boiling point, which varies depending on the liquid and atmospheric pressure. For water, this is 100°C at sea level.
- Influenced by Pressure: The boiling point can change with pressure; for instance, it is lower at high altitudes.
Conclusion
In summary, evaporation is a surface phenomenon that can happen at any temperature, while boiling is a bulk phenomenon that requires reaching a specific temperature. This distinction highlights why option 'C' is the correct answer: evaporation specifically occurs at the surface of the liquid.

Understanding Gas Behavior in a Syringe
When you pull the plunger of a syringe filled with gas, the behavior of the gas can be understood through the principles of gas laws.
Gas Expansion
- When you pull the plunger, you increase the volume of the syringe.
- According to Boyle's Law, if the temperature remains constant, the pressure of a gas decreases as the volume increases.
- This means the gas molecules have more space to move around, leading to expansion.
Why Option C is Correct
- As you pull the plunger, the gas expands to fill the increased volume within the syringe.
- The gas molecules will spread out, filling the available space equally.
Implications of Gas Expansion
- The expansion of gas occurs because gas particles are in constant motion and will occupy any available space.
- This behavior is a fundamental characteristic of gases, distinguishing them from liquids and solids.
Conclusion
In summary, pulling the plunger of a syringe filled with gas causes the gas to expand and fill the syringe. This not only illustrates the properties of gases but also reinforces the principles of gas laws, particularly Boyle's Law. Therefore, the correct answer is option 'C': The gas expands and fills the syringe.

Understanding States of Matter and Thermal Energy
When discussing the states of matter—solid, liquid, gas, and plasma—it's essential to understand how thermal energy affects the behavior of particles in each state.
1. Particle Behavior in Different States
- Solids:
- Particles are tightly packed.
- They vibrate in fixed positions, having low thermal energy.
- Liquids:
- Particles are close but can move past each other.
- They have more thermal energy than solids, allowing them to flow.
- Gases:
- Particles are far apart and move freely.
- They possess the highest thermal energy, leading to rapid motion and greater distances between particles.
- Plasma:
- Consists of ionized gases with free-moving charged particles.
- While plasma has high energy, its thermal energy is distributed differently than in gases.
2. Why Gases Have the Highest Thermal Energy
- Increased Motion:
- In gases, particles move rapidly and collide frequently. This high kinetic energy translates to greater thermal energy.
- Temperature Relation:
- The temperature of a gas is a measure of its average kinetic energy. Higher temperatures indicate higher thermal energy.
- Expansion and Compression:
- Gases expand to fill their containers, showcasing their high energy and the ability to overcome intermolecular forces.
Conclusion
In summary, gases have the highest thermal energy compared to liquids, solids, and plasma due to their rapid particle movement and increased distances between particles. Understanding these distinctions helps clarify the behavior of matter under different conditions.