All questions of A Journey through States of Water for Class 6 Exam

Why Does Water Vapor-Rich Air Rise?
Air containing water vapor rises primarily because it is lighter than the surrounding air. Here’s a detailed explanation:
Understanding Air Composition
- Air is made up of various gases, including nitrogen, oxygen, and water vapor.
- Water vapor is less dense than the other gases present in the atmosphere, particularly nitrogen and oxygen.
Density and Buoyancy
- When air contains water vapor, it becomes less dense overall.
- The molecular weight of water (H2O) is lower than that of the nitrogen (N2) and oxygen (O2) molecules that make up the majority of the atmosphere.
- This lower density creates a buoyant force, allowing the water vapor-laden air to rise.
Convection Process
- As the lighter, warmer air rises, it leads to a process known as convection.
- This rising air can cool and condense, forming clouds, which can eventually lead to precipitation.
Conclusion
- In summary, the primary reason that air containing water vapor rises is that it is lighter (less dense) than the surrounding air.
- This property plays a crucial role in weather patterns and the formation of clouds.
Understanding these basic principles of atmospheric science helps explain many weather phenomena we observe in our daily lives!

During condensation, water vapour loses heat and changes into liquid water.

Water vapour is the gaseous form of water and is invisible.

Evaporation is the process where liquid water gains heat and changes into water vapour.

Why Clothes Dry Faster on a Windy Day
When it comes to drying clothes, the weather plays a crucial role. On windy days, clothes tend to dry much faster, and the main reason for this is related to air movement and evaporation.
Understanding Evaporation
- Evaporation is the process where water changes from a liquid to a gas.
- This process requires energy, which is often provided by heat from the surroundings.
The Role of Wind
- On windy days, the movement of air helps remove the water vapor that forms around wet clothes.
- When air is still, the water vapor accumulates, creating a humid layer around the clothes. This layer slows down further evaporation.
Increased Air Movement
- Wind increases the rate of air movement, which continuously sweeps away the water vapor.
- This creates a lower humidity environment around the wet clothes, allowing more water to evaporate quickly.
Temperature's Influence
- While higher temperatures can also speed up evaporation, wind is the key factor on a windy day.
- Wind can enhance drying even at cooler temperatures because it improves evaporation efficiency.
Conclusion
In summary, the primary reason clothes dry faster on a windy day is due to the increased air movement that speeds up the evaporation process. This helps remove moisture from the clothes more efficiently, leading to quicker drying times.

Understanding Condensation
When a cold bottle is taken out of the fridge, water droplets form on its surface due to a process called condensation. Here’s how it works:
Humidity in the Air
- The air around us contains water vapor, which is invisible moisture.
- This water vapor exists in varying amounts depending on the humidity level in the environment.
Temperature Difference
- When the cold bottle is removed from the fridge, its surface temperature is significantly lower than the surrounding air.
- As warm air comes into contact with the cold surface of the bottle, the temperature of that air decreases.
Condensation Process
- Cooler air can hold less moisture than warm air.
- When the warm, humid air touches the cold bottle, it cools down rapidly.
- As the air cools, it loses its ability to hold moisture, causing the excess water vapor to change from a gas to a liquid.
Formation of Water Droplets
- This process creates tiny water droplets that accumulate on the surface of the bottle.
- Initially, these droplets are small and can merge to form larger drops, which eventually run down the sides of the bottle.
Conclusion
In summary, the correct answer is option 'C': water vapor in the air condenses on the cold surface of the bottle. This is a simple yet fascinating example of how temperature and humidity interact in our environment.