Q1. Matter is made up of tiny particles. This concept was illustrated through an activity involving the dissolution of:
a) Salt in oil
b) Sand in water
c) Salt in water
d) Sugar in alcohol
Answer: c) Salt in water
Explanation: The dissolution of salt in water was used to demonstrate that matter is made up of particles, as the salt disperses throughout the water.
Q2. The process of sublimation refers to the change of state from:
a) Solid to liquid
b) Liquid to gas
c) Solid to gas without passing through the liquid state
d) Gas to solid without passing through the liquid state
Answer: c) Solid to gas without passing through the liquid state
Explanation: Sublimation is the process where a solid changes directly into a gas without first becoming a liquid.
Q3. Which of the following is NOT a factor affecting the rate of evaporation?
a) Surface area
b) Temperature
c) Humidity
d) Density
Answer: d) Density
Explanation: The rate of evaporation is affected by surface area, temperature, and humidity but not directly by the density of the liquid.
Q4. The kinetic theory of matter states that particles:
a) Are static and closely packed in all states of matter
b) Move faster at higher temperatures in all states of matter
c) Only move in gases
d) Move slower in solids than in gases because they are not closely packed
Answer: b) Move faster at higher temperatures in all states of matter
Explanation: According to the kinetic theory of matter, the particles of an object move faster as the temperature increases, regardless of the state of matter.
Q5. The characteristic of particles of matter having space between them is demonstrated by:
a) Diffusion of ink in water
b) Sublimation of dry ice
c) Expansion of gases upon heating
d) Freezing of water into ice
Answer: a) Diffusion of ink in water
Explanation: The diffusion of ink in water illustrates that particles of matter have space between them, allowing the ink to spread throughout the water.
Q6. The latent heat of vaporization refers to the amount of heat energy required to:
a) Change 1 kg of liquid into solid at its freezing point
b) Change 1 kg of solid into gas at its sublimation point
c) Change 1 kg of gas into liquid at its condensation point
d) Change 1 kg of liquid into gas at its boiling point
Answer: d) Change 1 kg of liquid into gas at its boiling point
Explanation: The latent heat of vaporization is the heat energy needed to change 1 kg of a liquid into a gas at atmospheric pressure at its boiling point.
Q7. What determines the state (solid, liquid, gas) of a substance at a given temperature and pressure?
a) The chemical composition of the substance
b) The forces of attraction between the particles of the substance
c) The color of the substance
d) The amount of the substance
Answer: b) The forces of attraction between the particles of the substance
Explanation: The state of a substance at any given temperature and pressure is determined by the forces of attraction between its particles. These forces dictate whether the substance is in a solid, liquid, or gas state.
Q8. According to early Indian philosophers, everything in the universe is made up of how many basic elements?
a) Two
b) Three
c) Five
d) Seven
Answer: c) Five
Explanation: Early Indian philosophers classified matter into five basic elements — air, earth, fire, sky, and water, believing everything is made up of these elements.
Q9. The phenomenon where a gas changes directly into a solid without becoming a liquid first is known as:
a) Sublimation
b) Deposition
c) Condensation
d) Vaporization
Answer: b) Deposition
Explanation: Deposition is the direct change of a gas to a solid state without passing through the liquid state, opposite of sublimation.
Q10. When salt is dissolved in water, it demonstrates that particles of matter:
a) Are static and remain unchanged
b) Do not interact with each other
c) Are indivisible and impermeable
d) Are small and can get into the spaces between particles of water
Answer: d) Are small and can get into the spaces between particles of water
Explanation: Dissolving salt in water illustrates that particles of matter are small enough to move and fit into the spaces between water molecules.
Q11. The melting point of ice is an example of:
a) The temperature at which a liquid boils
b) The temperature at which a gas condenses
c) The temperature at which a solid melts
d) The temperature at which a liquid freezes
Answer: c) The temperature at which a solid melts
Explanation: The melting point, such as that of ice at 0°C (273.15 K), is the temperature at which a solid turns into a liquid.
Q12. Evaporation of water from a surface causes cooling because:
a) Water molecules absorb heat from the surface as they evaporate
b) The surface absorbs heat from the environment
c) Water molecules release heat into the surface as they evaporate
d) The surface releases heat to the water molecules
Answer: a) Water molecules absorb heat from the surface as they evaporate
Explanation: When water evaporates, it absorbs heat energy from its surroundings (or the surface it evaporates from), which causes cooling of the surface.
Q13. The rate of diffusion of particles in gases compared to liquids is:
a) The same
b) Slower
c) Faster
d) Non-existent
Answer: c) Faster
Explanation: Due to larger spaces between particles and their higher kinetic energy, particles in gases diffuse faster than those in liquids.
Q14. Which activity demonstrates that particles of matter are continuously moving?
a) Dissolving sugar in water
b) The spread of incense stick smoke in air
c) Freezing water into ice
d) Boiling water
Answer: b) The spread of incense stick smoke in air
Explanation: The movement of incense stick smoke through air, spreading its fragrance, showcases the continuous motion of particles in gases.
Q15. When heating a liquid to its boiling point, what happens to the temperature of the liquid during the phase change?
a) It continues to increase steadily
b) It decreases slightly before increasing again
c) It remains constant
d) It increases at a faster rate
Answer: c) It remains constant
Explanation: When a liquid reaches its boiling point, the temperature remains constant during the phase change from liquid to gas, as the added energy is used for the phase change, not for raising the temperature.
Q16. The process of changing a solid directly to gas is observed in which of the following substances?
a) Water
b) Carbon dioxide
c) Alcohol
d) Salt
Answer: b) Carbon dioxide
Explanation: Carbon dioxide undergoes sublimation, changing directly from solid (dry ice) to gas without passing through the liquid state.
Q17. What is the primary reason solids have a definite shape and volume?
a) The particles are not closely packed and can move freely
b) The particles have high kinetic energy
c) The forces of attraction between the particles are strong, keeping them in fixed positions
d) The particles are completely stationary
Answer: c) The forces of attraction between the particles are strong, keeping them in fixed positions
Explanation: Solids have a definite shape and volume because the particles are tightly packed in a fixed arrangement due to strong intermolecular forces of attraction.
Q18. What is latent heat of fusion?
a) The heat required to change a unit mass of gas to liquid without a temperature change
b) The heat required to change a unit mass of solid to gas without a temperature change
c) The heat required to change a unit mass of liquid to solid without a temperature change
d) The heat required to change a unit mass of solid to liquid without a temperature change
Answer: d) The heat required to change a unit mass of solid to liquid without a temperature change
Explanation: The latent heat of fusion is the amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point without a change in temperature.
Q19. Which of the following activities demonstrates the property of compressibility in gases?
a) Dissolving salt in water
b) Filling a balloon with air
c) Cutting a piece of wood
d) Boiling water to steam
Answer: b) Filling a balloon with air
Explanation: Filling a balloon with air demonstrates compressibility, as the gas (air) is compressed to fit into a confined space, showing that gases can be compressed much more easily than liquids or solids.
Q20. The phenomenon where liquids change to gas at the surface below boiling point is called:
a) Condensation
b) Vaporization
c) Evaporation
d) Sublimation
Answer: c) Evaporation
Explanation: Evaporation is the process where liquid turns into gas at the surface below its boiling point, occurring at any temperature when the surface molecules gain enough energy to enter the gas phase.
Q21. Why does a piece of ice float in water?
a) Ice has a higher density than water
b) Ice has a lower density than water
c) The particles in ice are not tightly packed
d) The water’s surface tension keeps the ice afloat
Answer: b) Ice has a lower density than water
Explanation: A piece of ice floats in water because it has a lower density than water. The crystalline structure of ice makes it less dense than liquid water, causing it to float.
Q22. Which of the following is not a change of state?
a) Melting
b) Dissolving
c) Freezing
d) Vaporization
Answer: b) Dissolving
Explanation: Dissolving is not considered a change of state. It is a process where a solute (like salt or sugar) is mixed with a solvent (like water), resulting in a solution without changing the states of matter of the substances involved.
Q23. The pressure exerted by gases is due to:
a) Their high density
b) The force of gravity on the gas particles
c) The particles colliding with the walls of the container
d) The evaporation of the gas
Answer: c) The particles colliding with the walls of the container
Explanation: The pressure exerted by a gas is due to the gas particles constantly moving and colliding with the walls of their container. These collisions result in a force exerted over the area of the container walls, which is observed as pressure.
Q24. During the process of melting, the temperature of a substance:
a) Decreases until the substance is fully melted
b) Increases continuously
c) Remains constant until the substance has fully melted
d) Fluctuates unpredictably
Answer: c) Remains constant until the substance has fully melted
Explanation: During the melting process, the temperature of a substance remains constant. This plateau occurs because the energy supplied as heat is used for the phase change from solid to liquid, not for increasing the temperature.
Q25. What role does humidity play in the process of evaporation?
a) It speeds up evaporation by adding more water vapor to the air
b) It does not affect the rate of evaporation
c) It slows down evaporation if the air is already full of water vapor
d) It increases the temperature, thereby increasing evaporation
Answer: c) It slows down evaporation if the air is already full of water vapor
Explanation: Humidity, the amount of water vapor present in the air, can slow down the rate of evaporation. When the air is highly humid, it already has a high concentration of water vapor, making it harder for additional water molecules to evaporate into the air.
Q26. The increase in wind speed affects the rate of evaporation by:
a) Decreasing the amount of water vapor in the air around the surface
b) Increasing the humidity level around the evaporating surface
c) Cooling down the temperature of the liquid
d) Increasing the temperature of the liquid
Answer: a) Decreasing the amount of water vapor in the air around the surface
Explanation: An increase in wind speed removes the air saturated with evaporated molecules from the surface of the liquid, lowering the concentration of water vapor near the surface. This allows more liquid to evaporate, hence increasing the rate of evaporation.
Q27. The process of a gas turning into a liquid is known as:
a) Freezing
b) Melting
c) Condensation
d) Sublimation
Answer: c) Condensation
Explanation: Condensation is the process by which gas turns into a liquid when it comes into contact with a cooler surface or cooler air, reducing its temperature below its dew point, or the temperature at which air becomes saturated with water vapor and can hold no more, leading to the conversion of vapor to liquid.
Q28. At what point does water reach its maximum density?
a) Just before it freezes
b) Immediately after it boils
c) While it is evaporating
d) At room temperature
Answer: a) Just before it freezes
Explanation: Water reaches its maximum density at approximately 4 degrees Celsius, just before it freezes. As it cools further and turns into ice, its density decreases, which is why ice floats on water.
Q29. Which of the following best describes the particles of a solid?
a) They are tightly packed and vibrate in place
b) They move freely and are far apart
c) They have no fixed volume and can be compressed easily
d) They spread out to fill the container they are in
Answer: a) They are tightly packed and vibrate in place
Explanation: The particles in a solid are closely packed in a fixed arrangement and can only vibrate in their fixed positions. This structure gives solids a definite shape and volume, and makes them relatively incompressible.
Q30. The kinetic energy of the particles of matter:
a) Decreases as the temperature decreases
b) Increases as the temperature increases
c) Remains constant regardless of temperature changes
d) Is only present in the particles of a gas
Answer: b) Increases as the temperature increases
Explanation: The kinetic energy of particles in matter increases as the temperature increases. This is because temperature is a measure of the average kinetic energy of the particles in a substance; as temperature rises, the particles move more rapidly.
Q31. Why do we see water droplets on the outside of a glass containing cold water?
a) Due to sublimation of water vapor into the glass
b) Because of evaporation of water from the glass
c) Due to condensation of water vapor from the air on the cooler surface of the glass
d) Because of the diffusion of water through the glass
Answer: c) Due to condensation of water vapor from the air on the cooler surface of the glass
Explanation: The water droplets form on the outside of a glass of cold water due to condensation. The cold surface of the glass cools the air around it below its dew point, causing water vapor in the air to condense into liquid water on the glass.
Q32. The process of changing liquid water into ice is known as:
a) Condensation
b) Vaporization
c) Freezing
d) Sublimation
Answer: c) Freezing
Explanation: Freezing is the process of changing liquid water into ice. This occurs when the temperature of the water drops below its freezing point, causing the water molecules to slow down and arrange themselves into a solid crystalline structure.
Q33. What is the effect of temperature on the solubility of gas in liquids?
a) Solubility increases as temperature increases
b) Solubility decreases as temperature increases
c) Temperature has no effect on the solubility of gases in liquids
d) Solubility first increases then decreases with temperature increase
Answer: b) Solubility decreases as temperature increases
Explanation: The solubility of gases in liquids generally decreases as the temperature increases. This is because higher temperatures provide more kinetic energy to the gas molecules, allowing them to escape more easily from the liquid.
Q34. The melting point of ice at atmospheric pressure is:
a) 0°C
b) 100°C
c) 4°C
d) -273°C
Answer: a) 0°C
Explanation: The melting point of ice, or the temperature at which ice turns into water at atmospheric pressure, is 0°C (32°F or 273.15K).
Q35. Why does hot food tend to cool down to room temperature?
a) Because of condensation
b) Due to radiation of heat to the surroundings
c) Because of sublimation
d) Due to absorption of heat by the surroundings
Answer: b) Due to radiation of heat to the surroundings
Explanation: Hot food cools down to room temperature primarily because of the radiation of heat to the cooler surroundings. This is a natural process where the heat energy is transferred from a hotter object to a cooler one until thermal equilibrium is reached.
Q36. The state of matter with the highest energy particles is:
a) Solid
b) Liquid
c) Gas
d) Plasma
Answer: c) Gas
Explanation: In the gas state, particles have the highest energy due to their rapid movement and the significant space between them, allowing for high-speed collisions and diffusion.
Q37. Which of the following is not a characteristic property of gases?
a) They have a definite shape
b) They fill their container completely
c) They are highly compressible
d) Their particles are far apart
Answer: a) They have a definite shape
Explanation: Gases do not have a definite shape; instead, they take the shape of their container. This is due to the significant spaces between their particles, allowing gases to expand and fill the container they are in.
Q38. The phenomenon where a solid directly changes into a gas upon heating, without passing through the liquid phase, is called:
a) Evaporation
b) Condensation
c) Sublimation
d) Deposition
Answer: c) Sublimation
Explanation: Sublimation is the process by which solids transform directly into gas upon heating, bypassing the liquid state. Examples include dry ice (solid CO2) turning into carbon dioxide gas.
Q39. The attractive force that exists between particles of matter is strongest in:
a) Gases
b) Liquids
c) Solids
d) Plasma
Answer: c) Solids
Explanation: The attractive forces between particles are strongest in solids, where particles are tightly packed in a fixed arrangement, giving solids a definite shape and volume.
Q40. Evaporation causes cooling because:
a) The process absorbs heat from the surroundings
b) The process releases heat into the surroundings
c) It increases the humidity of the surroundings
d) It decreases the kinetic energy of the remaining liquid particles
Answer: a) The process absorbs heat from the surroundings
Explanation: Evaporation causes cooling because the particles with the highest kinetic energy escape as gas, taking heat energy from the surroundings. This removal of heat cools the remaining liquid and the surface it evaporates from.
Q41. Which process is responsible for forming dew on grass in the early morning?
a) Freezing
b) Condensation
c) Evaporation
d) Sublimation
Answer: b) Condensation
Explanation: Dew forms on grass in the early morning through condensation. As the air cools overnight, water vapor in the air condenses into liquid water droplets on the cooler surfaces of grass blades.
Q42. When water vapor in the air condenses into liquid water, it forms:
a) Snow
b) Rain
c) Ice
d) Frost
Answer: b) Rain
Explanation: When water vapor in the air condenses, it forms tiny droplets that combine to become larger droplets, which can fall as rain if they grow heavy enough. Snow and frost are forms of precipitation that occur under different conditions, involving freezing.
Q43. Which factor does not affect the rate of evaporation?
a) Surface area
b) Pressure
c) Color of the liquid
d) Temperature
Answer: c) Color of the liquid
Explanation: The color of the liquid does not affect the rate of evaporation. Factors that influence evaporation include surface area, temperature, air pressure, and humidity, but not color.
Q44. When is water at its highest density?
a) At its boiling point
b) Just before it freezes
c) When it turns into steam
d) At room temperature
Answer: b) Just before it freezes
Explanation: Water reaches its highest density at approximately 4°C, just before it freezes. As it cools further and begins to freeze, its density decreases, which is why ice floats on water.
Q45. The process by which a gas turns into a solid without passing through the liquid phase is called:
a) Fusion
b) Deposition
c) Sublimation
d) Condensation
Answer: b) Deposition
Explanation: Deposition is the phase transition in which gas transforms directly into solid without passing through the intermediate liquid phase. It is the reverse process of sublimation.
Q46. Which state of matter has the least intermolecular space between particles?
a) Solid
b) Liquid
c) Gas
d) Both solid and liquid have the same intermolecular space
Answer: a) Solid
Explanation: Solids have the least intermolecular space between particles. The particles in a solid are tightly packed in a fixed structure, which gives solids a definite shape and volume.
Q47. The latent heat of vaporization is the amount of heat required to:
a) Change a unit mass of solid into liquid without a temperature change
b) Change a unit mass of gas into liquid at its condensation point
c) Change a unit mass of liquid into gas at its boiling point without a temperature change
d) Change a unit mass of liquid into solid without a temperature change
Answer: c) Change a unit mass of liquid into gas at its boiling point without a temperature change
Explanation: The latent heat of vaporization is the heat energy required to change 1 kg of a liquid into a gas at atmospheric pressure at its boiling point, without any change in temperature.
Q48. The kinetic theory of gases suggests that gas pressure is caused by:
a) The weight of the gas molecules
b) The constant motion and collisions of gas particles with container walls
c) The gravitational pull on the gas molecules
d) The intermolecular forces between gas molecules
Answer: b) The constant motion and collisions of gas particles with container walls
Explanation: The kinetic theory of gases explains that gas pressure is caused by the constant, random motion of gas particles, which collide with the walls of their container. These collisions result in the force that we measure as pressure.