Olympiad Test: Air And Water-2 - Class 6 MCQ

The correct answer is D. "Animals living in the water are not harmed during floods" is not a correct statement. Here is a detailed explanation:
Water availability:
- A: "Water available for use is very limited" is a correct statement. Water scarcity is a global issue, and the availability of freshwater for use is indeed limited.
Water evaporation:
- B: "Water evaporates from plants, animals, and oceans" is a correct statement. Water evaporates from various sources like plants, animals, and the vast expanse of oceans. This evaporation is an essential part of the water cycle.
Vegetation during droughts:
- C: "There is no vegetation during droughts" is a correct statement. Droughts, characterized by prolonged periods of little to no rainfall, can lead to the drying up of water sources and adversely affect vegetation. Lack of water during droughts can cause plants to wither and die.
Effects of floods on aquatic animals:
- D: "Animals living in the water are not harmed during floods" is not a correct statement. Floods can have significant impacts on aquatic ecosystems and the animals living in them. The sudden increase in water levels, strong currents, and sedimentation can disrupt habitats, displace animals, and even lead to the loss of life.
In conclusion, statement D is the incorrect one as animals living in the water can be harmed during floods.

Explanation:
When lime water (calcium hydroxide solution) is exposed to air and stirred, it turns milky due to the formation of a precipitate called calcium carbonate. This reaction occurs because air contains carbon dioxide, which reacts with calcium hydroxide to form calcium carbonate.
Here is a detailed explanation of the reaction:
1. Carbon Dioxide in the Air:
- The air we breathe contains approximately 0.04% carbon dioxide (CO2), which is a greenhouse gas.
- Carbon dioxide is produced by various natural and human activities, such as respiration, combustion, and decay of organic matter.
2. Reaction with Calcium Hydroxide:
- When carbon dioxide from the air dissolves in water, it forms carbonic acid (H2CO3).
- Carbonic acid reacts with calcium hydroxide (Ca(OH)2) in lime water to produce calcium carbonate (CaCO3).
- The chemical equation for this reaction is: CO2 + Ca(OH)2 → CaCO3 + H2O
3. Formation of Calcium Carbonate Precipitate:
- Calcium carbonate is insoluble in water and forms a white precipitate when it is produced in the reaction.
- The precipitate appears as a milky suspension in the lime water, giving it a cloudy or milky appearance.
- The milky appearance is due to the presence of tiny calcium carbonate particles suspended in the water.
4. Observing the Reaction:
- To observe the reaction, lime water is exposed to air and stirred to ensure proper mixing.
- As carbon dioxide from the air reacts with calcium hydroxide in the lime water, the solution turns milky.
- The milky appearance confirms the presence of carbon dioxide in the air.
Therefore, the correct answer is B: Carbon dioxide.

Greenhouse Effect and its Causes:
The greenhouse effect is a natural process that occurs when certain gases in the Earth's atmosphere trap heat from the sun, leading to an increase in the Earth's temperature. However, human activities have significantly contributed to the intensification of the greenhouse effect, leading to global warming and climate change.
Answer: Carbon dioxide (CO2) is the gas that causes the harmful greenhouse effect.
Explanation:
The detailed explanation for the harmful greenhouse effect caused by carbon dioxide is as follows:
- Greenhouse Effect: The greenhouse effect is a phenomenon where certain gases in the Earth's atmosphere trap heat from the sun and prevent it from escaping back into space. This trapped heat warms the Earth's surface and is essential for sustaining life on our planet.
- Greenhouse Gases: Greenhouse gases are the gases that contribute to the greenhouse effect. These gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases.
- Carbon Dioxide (CO2): Carbon dioxide is the most prevalent greenhouse gas emitted by human activities. It is released through the burning of fossil fuels such as coal, oil, and natural gas, as well as deforestation and certain industrial processes.
- Enhanced Greenhouse Effect: Human activities have significantly increased the concentration of carbon dioxide in the Earth's atmosphere. This enhancement of the greenhouse effect leads to a rise in global temperatures, known as global warming.
- Consequences: The consequences of the enhanced greenhouse effect and global warming include rising sea levels, melting polar ice caps, extreme weather events, shifts in ecosystems, and detrimental impacts on human health and well-being.
In conclusion, carbon dioxide is the gas that causes the harmful greenhouse effect. The increased concentration of carbon dioxide in the atmosphere, primarily due to human activities, leads to global warming and its associated consequences. It is crucial to reduce carbon dioxide emissions and adopt sustainable practices to mitigate the impacts of the greenhouse effect and combat climate change.

Explanation:
The water cycle is the continuous process of water evaporating from the Earth's surface, condensing into clouds, and then returning to the Earth as precipitation. This cycle can take place repeatedly because water has the property of changing from one state to another when it gains or loses heat.
Here is a detailed explanation of why water can change states and why this allows the water cycle to occur repeatedly:
1. Water exists in three states: solid (ice), liquid (water), and gas (water vapor). It can change between these states through the processes of freezing, melting, condensation, and evaporation.
2. When heat is added to water, it gains energy and its temperature increases. At 0°C, water freezes and turns into ice. At 100°C, water boils and turns into water vapor.
3. When heat is removed from water, it loses energy and its temperature decreases. Ice can melt into water, and water vapor can condense into liquid water droplets.
4. These changes in state are crucial to the water cycle. When heat from the sun causes water to evaporate from oceans, lakes, and rivers, it turns into water vapor. This water vapor rises into the atmosphere.
5. As the water vapor rises, it cools down and condenses into tiny water droplets or ice crystals, forming clouds.
6. When the droplets or ice crystals in the clouds become too heavy, they fall back to the Earth's surface as precipitation, including rain, snow, sleet, or hail.
7. The precipitation replenishes water sources such as rivers, lakes, and underground aquifers, and the cycle starts again.
In conclusion, the water cycle can take place repeatedly because water has the ability to change from one state to another when it gains or loses heat. This allows water to evaporate, condense, and precipitate, ensuring a continuous cycle that is vital for the Earth's ecosystems and the survival of living things.

Reducing Air Pollution on the Road

Air pollution on the road can be reduced by implementing various measures. Some of the effective solutions include:

• Encouraging the use of CNG in vehicles: Promoting the use of Compressed Natural Gas (CNG) as a fuel for vehicles can significantly reduce air pollution. CNG produces fewer emissions compared to conventional fossil fuels, resulting in cleaner air quality.



• Reducing the number of vehicles on the road: Implementing strategies to reduce the number of vehicles on the road can help in decreasing air pollution levels. This can be achieved through initiatives like carpooling, promoting public transportation, and encouraging walking or cycling for shorter distances.



• Planting trees on roadsides: Planting trees along roadsides can act as a natural barrier to air pollution. Trees absorb carbon dioxide and release oxygen, helping to improve air quality. They also act as a physical barrier, reducing the direct exposure of pollutants to pedestrians and nearby residents.



• Implementing strict emission standards: Enforcing stringent emission standards for vehicles can play a crucial role in reducing air pollution. This can be done by regularly inspecting vehicles for emissions compliance and taking appropriate actions against vehicles that exceed the permissible limits.



• Promoting electric vehicles: Encouraging the adoption of electric vehicles (EVs) can significantly reduce air pollution on the road. EVs produce zero emissions while driving, thus contributing to cleaner air quality and lower levels of pollution.

In conclusion, to effectively reduce air pollution on the road, a combination of measures such as promoting the use of CNG, reducing the number of vehicles, planting trees, implementing strict emission standards, and promoting electric vehicles should be implemented.

The presence of air causes the following:
Flying of birds:
- Birds are able to fly because of the presence of air.
- The air provides the necessary lift and support for birds' wings, allowing them to stay in the air and maneuver.
- The movement of air over the wings creates an upward force called lift, which enables birds to stay airborne.
Dispersal of seeds:
- Air plays a crucial role in the dispersal of seeds.
- Many plants have adaptations that allow their seeds to be carried by the wind.
- As the wind blows, it carries the lightweight seeds to new locations, helping plants spread and colonize different areas.
Generating electricity:
- Air can be used to generate electricity through various methods.
- Wind turbines harness the power of moving air to generate electricity.
- The force of the wind turns the blades of the turbine, which in turn rotates a generator to produce electricity.
All of them:
- The presence of air is necessary for all three scenarios described above.
- Flying of birds, dispersal of seeds, and generating electricity all depend on the properties and characteristics of air.
In conclusion, the correct answer is D: All of them. The presence of air is essential for flying of birds, dispersal of seeds, as well as generating electricity through wind power.