All questions of Air around Us for Class 6 Exam

Combustibility is the ability of a substance to burn or ignite when exposed to a flame or heat source. Among the given options, hydrogen is the only substance that is combustible. Let's explore why hydrogen is combustible and why the other options are not.

1. Hydrogen:
Hydrogen is a highly flammable gas and is considered combustible. It has a low ignition energy, meaning it can easily ignite and burn in the presence of a spark or flame. When hydrogen combines with oxygen (in the air), it forms an explosive mixture that can be easily ignited. This reaction is highly exothermic, releasing a large amount of heat energy.

2. Oxygen:
Oxygen is not combustible. It is a non-flammable gas that supports combustion. This means that oxygen is necessary for other substances to burn, but it does not burn itself. Oxygen supports combustion by reacting with combustible materials, such as fuels, to produce heat and light. It acts as an oxidizer, allowing other substances to burn more readily.

3. Carbon dioxide:
Carbon dioxide is not combustible. It is a non-flammable gas that does not support combustion. Carbon dioxide does not react with heat or flame, and it does not burn. In fact, carbon dioxide is often used as a fire extinguisher because it displaces oxygen and removes the necessary component for combustion.

4. All of these:
The correct answer is option 'C' - Hydrogen. Only hydrogen is combustible among the given options. Oxygen and carbon dioxide are non-combustible gases.

Dipping an inverted bottle into water shows that air occupies space. When the bottle is submerged, the air inside the bottle prevents water from entering, creating bubbles as the air escapes. This simple demonstration effectively proves that air takes up space and cannot be seen but occupies volume.

The correct answer is option 'D' which states that the percentage of nitrogen in air is 78%. Let's understand why this is the correct answer.

**Introduction:**
Air is a mixture of various gases, with the two most abundant gases being nitrogen and oxygen. Nitrogen is an essential component of the Earth's atmosphere and plays a crucial role in supporting life on Earth.

**Composition of Air:**
Air is composed of several gases, including nitrogen, oxygen, carbon dioxide, and trace amounts of other gases. The exact composition of air can vary slightly depending on location and other factors, but on average, the composition is as follows:

- Nitrogen (N₂): Approximately 78%
- Oxygen (O₂): Approximately 21%
- Carbon Dioxide (CO₂): Approximately 0.04%
- Trace Gases (Argon, Neon, Methane, etc.): Approximately 1%

**Explanation:**
Nitrogen gas (N₂) makes up the majority of the Earth's atmosphere, accounting for approximately 78% of the total volume of air. This means that out of every 100 units of air, around 78 units are nitrogen gas.

Oxygen gas (O₂) is the second most abundant gas in the atmosphere, making up approximately 21% of the total volume of air. This accounts for the remaining percentage of air composition.

The other gases present in the atmosphere, such as carbon dioxide (CO₂) and trace gases like argon and methane, make up a very small percentage of the total composition, collectively accounting for approximately 1%.

**Conclusion:**
In conclusion, the correct answer is option 'D' which states that the percentage of nitrogen in air is 78%. This makes nitrogen the most abundant gas in the Earth's atmosphere, while oxygen is the second most abundant. Understanding the composition of air and the role of nitrogen is important in various scientific and environmental contexts.

Atmosphere
The layer of air around the Earth's surface is called the atmosphere. It is a crucial component of the Earth's system and plays a vital role in sustaining life on our planet. Let's delve deeper into the details of the Earth's atmosphere.

Composition of the Atmosphere
- The Earth's atmosphere is primarily composed of nitrogen (about 78%) and oxygen (about 21%).
- Other gases such as carbon dioxide, argon, and water vapor make up the remaining 1%.

Layers of the Atmosphere
- The atmosphere is divided into five main layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
- Each layer has distinct characteristics and plays a specific role in regulating temperature and weather patterns on Earth.

Functions of the Atmosphere
- The atmosphere helps regulate the Earth's temperature by trapping heat from the sun and preventing it from escaping into space.
- It also protects the Earth's surface from harmful solar radiation and cosmic rays.
- The atmosphere is essential for the water cycle, as it enables the formation of clouds and precipitation.

Conclusion
In conclusion, the atmosphere is a crucial layer of air surrounding the Earth that sustains life and regulates the planet's climate. Understanding the composition and functions of the atmosphere is essential for comprehending the Earth's interconnected systems and how they impact our daily lives.

When air in a sealed container is heated, it expands and exerts more pressure. This is because heating causes the air molecules to move faster and spread out, increasing the volume and pressure within the container. This principle is used in various applications, including hot air balloons and pressure cookers.

Carbon dioxide is a major contributor to the greenhouse effect. It traps heat in the Earth's atmosphere, leading to global warming. Carbon dioxide levels have increased due to human activities such as burning fossil fuels and deforestation, impacting the climate and environment.

How does dust affect the air quality?
Dust particles in the air can have various negative effects on air quality, making it harmful to breathe and affecting overall environmental conditions.

1. Particulate matter:
- Dust particles can contribute to the formation of particulate matter in the air, which can be harmful when inhaled.
- Particulate matter can penetrate deep into the lungs and cause respiratory issues, especially in people with pre-existing conditions like asthma or lung disease.

2. Allergens:
- Dust can contain allergens like pollen, mold spores, and pet dander, which can worsen allergy symptoms and respiratory problems.

3. Air pollution:
- Dust can interact with other pollutants in the air, such as vehicle emissions and industrial pollutants, to form smog and other harmful compounds.
- This can lead to poor air quality, reduced visibility, and health problems for people exposed to the polluted air.

4. Climate change:
- Dust particles can also impact the Earth's climate by affecting the amount of sunlight that reaches the surface and contributing to the greenhouse effect.
- This can lead to changes in temperature patterns and weather conditions, affecting both human health and the environment.
In conclusion, dust can significantly degrade air quality by increasing levels of particulate matter, allergens, air pollution, and contributing to climate change. It is important to address sources of dust and take measures to improve air quality for the health and well-being of both humans and the environment.

Nitrogen is the most abundant gas in the air, making up about 78% of the atmosphere. It is a major component of the air we breathe and is important for various biological processes, though it does not support combustion. Nitrogen acts as a buffer to prevent the air from becoming too reactive.

The primary function of the Earth's atmosphere is to block harmful radiation from the sun, protecting living organisms from ultraviolet (UV) rays. It also helps in regulating temperature and supporting life by providing essential gases like oxygen. The atmosphere plays a critical role in maintaining the Earth's climate and weather systems.

Oxygen is essential for supporting burning (combustion) and respiration in living organisms. Without oxygen, fires would not burn and animals and plants could not survive. Oxygen is crucial for the processes that keep us and other living things alive. An interesting fact is that oxygen makes up about 21% of the Earth's atmosphere, which is just enough to sustain life.

Plants use carbon dioxide for photosynthesis, a process in which they convert carbon dioxide and sunlight into glucose and oxygen. This process is essential for plant growth and also helps maintain the balance of carbon dioxide and oxygen in the atmosphere.

Plants and Animals Dependence on Each Other for Gases in the Atmosphere
Plants and animals have a mutual dependence on each other for gases in the atmosphere, primarily oxygen and carbon dioxide.
- Plants produce oxygen: Through the process of photosynthesis, plants take in carbon dioxide from the atmosphere and water from the soil to produce oxygen. This oxygen is released back into the atmosphere as a byproduct and is essential for the survival of animals, including humans.
- Animals produce carbon dioxide: Animals, including humans, take in oxygen from the atmosphere and release carbon dioxide through the process of respiration. This carbon dioxide is then used by plants during photosynthesis to produce oxygen, creating a continuous cycle of gas exchange between plants and animals.
This interdependence between plants and animals ensures a balance of gases in the atmosphere, allowing both to thrive. If this balance is disrupted, it can have detrimental effects on both plant and animal populations, as well as the overall health of the ecosystem.

A weather cock (or weathervane) shows the direction in which the wind is blowing. It is a tool used to determine wind direction, which can help in weather forecasting and understanding local weather patterns. Wind direction is crucial for various weather-related applications.

Understanding the Properties of Air
Air is a mixture of various gases, primarily nitrogen and oxygen, along with trace amounts of other gases. Let's explore why option 'D' is the correct answer regarding the properties of air.
Air Composition Varies
- Variation in Composition: The composition of air can change based on several factors, including location, altitude, and environmental conditions. For instance:
- Urban areas may have higher levels of pollutants like carbon monoxide and sulfur dioxide.
- Coastal regions can have higher humidity levels, affecting the air's moisture content.
- High-altitude locations may have thinner air with reduced oxygen levels.
Other Statements Explained
- Good Conductor of Electricity:
- Air is generally not a good conductor of electricity. In fact, it is an insulator unless ionized (as in the case of lightning).
- Good Conductor of Heat:
- Air is a poor conductor of heat compared to solids and liquids. It is often used as an insulator (like in double-glazed windows) due to its low thermal conductivity.
- Translucent:
- Air itself is not translucent; rather, it is transparent. It allows light to pass through without scattering.
Conclusion
In conclusion, the correct answer is option 'D' as the composition of air varies from place to place due to environmental factors, human activity, and geographical differences. Understanding these properties helps us appreciate the complexities of the atmosphere surrounding us.