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

When Rachit blows air into the bottle, the air pressure inside the bottle increases, which makes it difficult for the balloon to inflate fully if the mouthpiece is tightly sealed over the opening. For the balloon to inflate more, there needs to be a way for the air to escape from the bottle, allowing the air pressure inside the balloon to increase and make it expand further.

• Option A (Make a hole in the balloon) would cause air to escape from the balloon, preventing it from inflating at all.
• Option B (Pour water into the balloon) is not a good idea because water cannot be compressed like air, and it would prevent the balloon from inflating fully.
• Option D (Use a glass bottle) would not make a significant difference in the balloon's inflation, as the material of the bottle doesn't directly affect how the balloon inflates unless it’s tightly sealed or not airtight.

Making a hole in the bottle allows air to escape, reducing the air pressure in the bottle and enabling the balloon to inflate more easily.

• 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.

Lime water turns milky when it reacts with carbon dioxide (CO₂) in the air. The reaction produces calcium carbonate (CaCO₃), which is a white precipitate, making the lime water appear milky.

The chemical reaction is: CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

This reaction demonstrates that carbon dioxide is present in the air, as it is responsible for the milky appearance.

Carbon dioxide (CO₂) is a major greenhouse gas that contributes to the greenhouse effect, which leads to global warming. It traps heat in the Earth's atmosphere, preventing it from escaping into space. This results in an increase in Earth's average temperature, which is a major factor in climate change.

• Oxygen (A) and Nitrogen (D) are gases present in the atmosphere but do not contribute significantly to the greenhouse effect.
• Hydrogen (C) is not a major component of the atmosphere and does not play a significant role in the greenhouse effect either.

Thus, the correct answer is B) Carbon dioxide.

The water cycle is a continuous process because water can change between different states—liquid, gas, and solid—when it gains or loses heat. This flexibility in state change is the key to the water cycle's repetition:

• Evaporation occurs when water absorbs heat and changes from liquid to gas (water vapor).
• Condensation happens when water vapor cools down and changes back to liquid.
• Freezing occurs when water loses heat and turns into ice.
• Melting occurs when ice absorbs heat and turns back into liquid water.

This ability to change states as a result of heat exchange allows the water cycle to take place repeatedly.

The other options do not explain the repeating nature of the water cycle:

• A: Freezing at 0°C and boiling at 100°C describes the temperature at which water changes states but does not explain the cycle.
• B: While water is incompressible, this does not directly explain the cycling of water.
• C: While water is essential for life, this does not explain why the water cycle occurs repeatedly.

Thus, the correct answer is D) Can change from one state to another when it gains or loses heat.

When the paper wheel is placed over a lighted candle, the heat from the flame heats up the surrounding air. As the air becomes hot, it becomes less dense and rises. The rising hot air causes a movement of air currents, and this moving air (which has kinetic energy) exerts force on the paper wheel, causing it to rotate. This is a classic example of how the movement of air due to differences in temperature (convection) can cause motion.

Option B (The hot air rises and the potential energy of the moving air causes the wheel to turn) is incorrect because it refers to "potential energy" in this context. Potential energy typically refers to energy due to position, not motion. In this case, it is the kinetic energy of the moving air that causes the wheel to turn.

Therefore, the correct reason is Option A, as it accurately describes the process involving the heat-induced movement of air and the resulting kinetic energy that makes the wheel spin.

The composition of air is approximately as follows:

• About 78% of the atmosphere is nitrogen (N₂).
• About 21% is oxygen (O₂).
• The remaining 1% consists of other gases, such as argon, carbon dioxide, neon, helium, and trace amounts of other gases.

So, the most accurate description of air, based on these proportions, is Option A, where one-fifth (about 21%) is oxygen and four-fifths (about 78%) is nitrogen and other gases.

Each of the options contributes to reducing air pollution on the road:

• A: Encouraging the use of CNG (Compressed Natural Gas) in vehicles helps reduce air pollution because CNG is a cleaner fuel compared to petrol or diesel, producing fewer harmful emissions like carbon monoxide and nitrogen oxides.

• B: Reducing the number of vehicles on the road helps decrease the overall emissions of pollutants such as carbon dioxide, nitrogen oxides, and particulate matter, leading to cleaner air.

• C: Planting trees on roadsides can help absorb carbon dioxide and other pollutants from the air, acting as natural air purifiers and improving air quality.

Thus, all of these actions combined will effectively help reduce air pollution on the roads, making the correct answer D) All of them.

The presence of air plays a role in all the given processes:

• A: Flying of birds: Birds rely on air for flight, using the force of air against their wings to generate lift.
• B: Dispersal of seeds: Air (wind) helps in the dispersal of many types of seeds, allowing them to travel long distances from the parent plant.
• C: Generating electricity: Air is essential for wind power generation. Wind turbines use the movement of air to generate electricity.

Thus, all of these processes are influenced by the presence of air, making the correct answer D) All of them.

The cyclic movement of water from the atmosphere to the Earth and back to the atmosphere through various processes is called the water cycle. Three main steps are involved in the water cycle that is evaporation, condensation, and precipitation.

During the water cycle, water from the earth is circulated in the form of water vapour by evaporation and condenses to form clouds and precipitates back to earth in the form of rain, snow.

Hence, option C is correct.