States Of Water

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Q1. The three states of water are:
Water exists in three physical states: solid (ice), liquid (water) and gas (water vapour). These states are interconvertible through processes like melting, freezing, evaporation and condensation. The state of water depends on the temperature and pressure.
Q2. The solid state of water is called:
The solid state of water is called ice. It is formed when water is cooled below its freezing point, which is 0°C. In this state, water molecules are tightly packed in a regular pattern.
Q3. The liquid state of water is called:
The liquid state of water is simply called water. It is the most common state of water on Earth and is found in rivers, lakes, oceans and groundwater. In this state, water molecules can move freely but are still close together.
Q4. The gaseous state of water is called:
The gaseous state of water is called water vapour. It is an invisible gas that is formed when water evaporates or boils. Water vapour is present in the air around us and is an important part of the water cycle.
Q5. The process by which a liquid changes into a gas is called:
Evaporation is the process by which a liquid changes into a gas at a temperature below its boiling point. It occurs on the surface of the liquid and is caused by the absorption of heat. Evaporation is a key part of the water cycle.
Q6. The process by which a gas changes into a liquid is called:
Condensation is the process by which water vapour (gas) changes into liquid water. This happens when water vapour comes into contact with a cool surface and loses heat. Condensation is responsible for the formation of clouds, dew and fog.
Q7. The process by which a liquid changes into a solid is called:
Freezing is the process by which a liquid changes into a solid when it is cooled. For water, freezing occurs at 0°C (32°F). During freezing, water molecules slow down and arrange themselves into a rigid, crystalline structure, forming ice.
Q8. The process by which a solid changes into a liquid is called:
Melting is the process by which a solid changes into a liquid when it is heated. For ice, melting occurs at 0°C (32°F). During melting, the rigid structure of the solid breaks down as molecules gain energy and move more freely.
Q9. The continuous movement of water from the Earth’s surface to the atmosphere and back is called the:
The water cycle, also known as the hydrological cycle, is the continuous movement of water on, above and below the Earth’s surface. It involves processes like evaporation, condensation, precipitation and collection. This cycle is essential for maintaining life on Earth.
Q10. The amount of water vapour present in the air is called:
Humidity is the amount of water vapour present in the air. It is usually expressed as a percentage of the maximum amount of water vapour the air can hold at a given temperature. High humidity makes the air feel sticky, while low humidity makes it feel dry.
Q11. When water evaporates, it disappears into the air as:
When water evaporates, it changes from a liquid to a gas called water vapour. This water vapour mixes with the air and becomes invisible. The water has not disappeared completely; it has simply changed its state.
Q12. Water disappears from wet clothes when they dry because:
Wet clothes dry because the water in them evaporates into the air. The heat from the sun or the air provides the energy needed for water molecules to escape into the atmosphere. This is a common example of evaporation in daily life.
Q13. We feel cooler under a fan because:
When we sit under a fan, the moving air increases the rate of evaporation of sweat from our skin. As sweat evaporates, it takes heat from our body, giving us a cooling effect. The fan itself does not cool the air; it speeds up evaporation.
Q14. The cooling effect of evaporation is used in:
The cooling effect of evaporation is used in many everyday applications. Air conditioners and refrigerators use evaporation to remove heat. Water stored in earthen pots stays cool because water seeps through the pores and evaporates, taking heat away from the water inside.
Q15. A glass tumbler containing cold water and ice cubes has water droplets on its outer surface because:
When a glass tumbler containing cold water and ice is kept in a room, the cold surface cools the air around it. The water vapour in the warm air condenses on the cold surface of the glass, forming tiny water droplets. This is a common example of condensation.
Q16. Clouds are formed by the process of:
Clouds are formed when water vapour in the air rises and cools. As the water vapour cools, it condenses into tiny water droplets around dust particles. When millions of these droplets come together, they form clouds.
Q17. The process by which water changes from a liquid to a gas at its boiling point is called:
Boiling is the process by which a liquid changes into a gas at its boiling point. The boiling point of water is 100°C at normal atmospheric pressure. During boiling, bubbles of vapour form throughout the liquid, not just on the surface.
Q18. The process of changing water vapour into liquid water by cooling is called:
Condensation is the process by which water vapour changes into liquid water when it is cooled. This is how clouds are formed and how dew appears on grass in the morning. Condensation is the opposite of evaporation.
Q19. The process by which ice changes directly into water vapour without becoming liquid is called:
Sublimation is the process by which a solid changes directly into a gas without passing through the liquid state. In the case of water, ice can sublime directly into water vapour under certain conditions. This is why snow can disappear without melting.
Q20. The formation of dew on grass in the morning is an example of:
Dew forms on grass in the morning when the surface temperature drops below the dew point. The water vapour in the air condenses on the cool grass blades, forming tiny drops of water. This is a natural example of condensation.
Q21. Evaporation can be faster when:
Evaporation is faster at higher temperatures because water molecules have more energy to escape into the air. It is also faster when there is more wind, as the moving air carries away water vapour, and when humidity is low, because the air can hold more water vapour.
Q22. Evaporation can be slower when:
Evaporation is slower when the temperature is low, when humidity is high (air is already saturated with moisture), and when there is no wind to carry away the water vapour. In such conditions, water takes longer to dry.
Q23. The difference in the properties of water in solid, liquid and gaseous states is due to:
The properties of water in different states depend on the arrangement and movement of molecules, which are affected by temperature and pressure. In ice, molecules are tightly packed; in liquid water, they are less tightly packed; and in water vapour, they are far apart and move freely.
Q24. In the solid state (ice), water molecules are:
In the solid state (ice), water molecules are tightly packed in a fixed, regular pattern called a crystalline structure. They vibrate in place but do not move freely. This gives ice its rigid shape and volume.
Q25. In the liquid state (water), molecules are:
In the liquid state, water molecules are close together but can move and slide past each other. They have more energy than in the solid state but less than in the gaseous state. This allows liquid water to flow and take the shape of its container.
Q26. In the gaseous state (water vapour), molecules are:
In the gaseous state, water molecules are far apart and move very fast in all directions. They have the highest amount of energy among the three states. This is why water vapour fills any container it is in and has no fixed shape or volume.
Q27. Ice floats on water because:
Ice floats on water because it is less dense than liquid water. When water freezes, it expands and its molecules form a structure that takes up more space. This makes ice lighter than an equal volume of liquid water.
Q28. The boiling point of water is:
The boiling point of water is 100°C at normal atmospheric pressure. At this temperature, water changes from a liquid to a gas (water vapour or steam). Boiling occurs throughout the liquid, not just at the surface.
Q29. The melting point of ice is:
The melting point of ice is 0°C. At this temperature, ice changes from a solid to a liquid (water). This is the temperature at which ice begins to melt and is also the freezing point of water.
Q30. The freezing point of water is:
The freezing point of water is 0°C. At this temperature, water changes from a liquid to a solid (ice). The freezing point and the melting point of water are the same temperature.
Q31. Rain is caused when:
Rain occurs when water vapour in the atmosphere condenses to form tiny water droplets that come together to form clouds. When these droplets become too heavy to remain suspended, they fall to the Earth as raindrops. Rain is an important part of the water cycle.
Q32. Rainwater is considered pure because:
Rainwater is considered pure because it is formed by the condensation of water vapour in the atmosphere. During condensation, impurities like salts and minerals are left behind, making rainwater relatively pure. However, it can pick up dust and gases from the air as it falls.
Q33. The water that falls from the atmosphere to the Earth in any form is called:
Precipitation is the general term for water that falls from the atmosphere to the Earth in any form, including rain, snow, hail and sleet. Rain is the most common form of precipitation. Precipitation is a key step in the water cycle.
Q34. The process by which plants release water vapour into the air is called:
Transpiration is the process by which plants release water vapour into the atmosphere through tiny pores in their leaves called stomata. This is an important part of the water cycle, as it adds moisture to the air, which can later condense to form clouds.
Q35. Unclean water is harmful because it can contain:
Unclean water can contain disease-causing germs (bacteria, viruses, parasites), harmful chemicals (pesticides, heavy metals) and toxic substances. Drinking or using such water can cause serious diseases like cholera, typhoid and diarrhoea. This is why water purification is essential.
Q36. Water can be purified by:
Water can be purified by boiling, which kills germs; by filtration, which removes insoluble impurities; and by using chlorine, which kills harmful microorganisms. These methods help make water safe for drinking.
Q37. The water cycle is driven by energy from the:
The water cycle is driven by energy from the Sun. The Sun’s heat causes water to evaporate from oceans, rivers and lakes, and it also drives the processes of condensation and precipitation. Without the Sun, the water cycle would not exist.
Q38. Warm water evaporates faster than cold water because:
Warm water evaporates faster because the water molecules in warm water have more kinetic energy. This allows them to escape from the surface of the liquid more easily. Heating water increases the rate of evaporation.
Q39. We feel cooler when we sweat because:
When we sweat, the water on our skin evaporates. This evaporation process requires energy (heat), which is taken from our body. As a result, our body cools down. This is why sweating is important for temperature regulation.
Q40. Water vapour is invisible because:
Water vapour is invisible because it is a gas and does not have a colour. We cannot see it, but it is present in the air around us. It only becomes visible when it condenses into tiny water droplets or when it turns into steam.
Q41. When water is heated, it changes from liquid to gas. This is called:
When water is heated, it changes from liquid to gas through evaporation. If heated to its boiling point (100°C), it boils and becomes steam. Evaporation occurs on the surface of the liquid at any temperature.
Q42. When water vapour is cooled, it changes to liquid. This is called:
When water vapour is cooled, it changes to liquid through condensation. This happens when the vapour loses heat energy. Condensation is visible as water droplets on cold surfaces or as clouds in the sky.
Q43. The formation of clouds is an example of:
Clouds are formed by the condensation of water vapour in the atmosphere. As warm, moist air rises and cools, the water vapour condenses into tiny droplets around dust particles. When many droplets come together, they form a visible cloud.
Q44. The water that seeps into the ground is called:
Groundwater is the water that seeps into the ground through the soil and accumulates in underground layers called aquifers. It is an important source of fresh water for drinking and irrigation. Groundwater is part of the water cycle.
Q45. The process by which water vapour changes into ice directly is called:
Deposition is the process by which water vapour changes directly into ice without becoming liquid water first. This is how frost and snowflakes are formed. Deposition is the opposite of sublimation.
Q46. The process by which water in the form of snow or ice changes directly into water vapour is called:
Sublimation is the process by which a solid changes directly into a gas without becoming a liquid. In the case of water, ice or snow can sublime into water vapour under certain conditions. This is why snow can disappear on cold, sunny days without melting.
Q47. The main source of water on Earth is:
Oceans are the main source of water on Earth, containing about 97% of all the water on the planet. However, this water is salty and not directly suitable for drinking. The water cycle helps distribute fresh water to other parts of the Earth.
Q48. The process by which water changes from a gas to a liquid and then to a solid is called:
Water can change from a gas to a liquid through condensation and then to a solid through freezing. This is how water vapour in clouds can form rain and snow. These changes are part of the water cycle.
Q49. The amount of water on Earth is:
The total amount of water on Earth is constant. It is neither increasing nor decreasing; it only changes state and moves through the water cycle. The same water has been circulating for millions of years.
Q50. The evaporation of water from the surface of oceans, rivers and lakes is caused by:
The Sun is the main cause of evaporation from the surface of oceans, rivers and lakes. Solar radiation heats the water, giving its molecules enough energy to escape into the air as water vapour. This is the first step of the water cycle.
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Q51. Water in an earthen pot remains cool because:
Water in an earthen pot remains cool because water seeps through the tiny pores in the clay and evaporates from the outer surface. This evaporation takes heat from the pot and the water inside, keeping it cool. This is a traditional method of cooling water.
Q52. The cooling effect of evaporation is greater when:
The cooling effect of evaporation is greater when the temperature is high, humidity is low and wind is blowing. These conditions increase the rate of evaporation, which removes more heat from the surface. This is why we feel cool when we sweat on a hot, windy day.
Q53. When water is cooled, it changes from liquid to solid. This is called:
When water is cooled, it changes from a liquid to a solid through freezing. This happens at 0°C, when the molecules slow down and form a rigid structure. Freezing is the opposite of melting.
Q54. When water is heated, it changes from solid to liquid. This is called:
When water is heated, it changes from a solid (ice) to a liquid (water) through melting. This happens at 0°C, when the molecules gain enough energy to break free from their fixed positions. Melting is the opposite of freezing.
Q55. Water vapour in the air condenses on cold surfaces because:
Water vapour condenses on cold surfaces because the cold surface cools the vapour and removes heat from it. When the vapour loses enough heat, it changes from a gas to a liquid. This is why we see droplets on a cold glass of water.
Q56. The water cycle helps in:
The water cycle is essential for maintaining the freshwater supply on Earth, regulating the climate and distributing water to different regions. It ensures that water is continuously recycled and available for all living organisms. Without the water cycle, life on Earth would not be possible.
Q57. The cloud droplets come together to form larger drops and fall as rain. This is called:
Precipitation is the process by which water falls from clouds to the Earth in the form of rain, snow, sleet or hail. When cloud droplets join together and become heavy, gravity pulls them down as precipitation. Rain is the most common form of precipitation.
Q58. The state of water can be changed by:
The state of water can be changed by heating (melting and evaporation), cooling (freezing and condensation) and changing pressure. For example, increasing pressure can change water vapour to liquid, and decreasing pressure can cause water to boil at a lower temperature.
Q59. The invisible water vapour in the air is:
Water vapour is a gas, which is a state of matter. Even though it is invisible, it is matter because it has mass and occupies space. It is an important part of the Earth’s atmosphere.
Q60. The water cycle is continuous because:
The water cycle is continuous because water is constantly evaporating from the Earth’s surface, condensing into clouds and returning to the Earth as precipitation. The Sun provides the energy for this process. This cycle has been going on for billions of years and will continue as long as the Sun shines.