Olympiad Test: Air Around Us - Class 6 MCQ

Oxygen is essential for several processes, including:

• Combustion: This process requires oxygen to burn materials.
• Respiration: Living organisms need oxygen to convert food into energy.
• Oxidation: This chemical reaction involves oxygen and is crucial for various biological and chemical processes.

Therefore, all these processes depend on the presence of oxygen.

The density of air decreases with an increase in altitude.

This means that as you go higher, the air becomes thinner. Here are some key points to understand this concept:

• The atmosphere is a layer of air surrounding the Earth.
• At higher altitudes, there are fewer air molecules, making the air less dense.
• This decrease in density affects various activities, such as mountaineering, where climbers may need extra oxygen.
• Understanding air density is important for weather patterns and aviation.

When we heat water, we find bubbles coming from it. This shows that

When water is heated, it releases tiny bubbles due to the presence of dissolved air. Here’s a clearer breakdown:

• As water heats up, the air dissolved in it escapes first.
• Continued heating causes the water to turn into vapour.
• Eventually, the water reaches its boiling point and begins to boil.

It's important to note that the solubility of gases decreases as the temperature increases. This means that warmer water holds less air, leading to the formation of bubbles.

Plants play a crucial role in the oxygen cycle. They release oxygen through the process of photosynthesis, which is essential for maintaining the balance of oxygen in the atmosphere.

• During photosynthesis, plants convert carbon dioxide and sunlight into food and oxygen.
• Plants produce more oxygen than they consume for their own respiration.
• This process is vital for the survival of animals, as they rely on oxygen produced by plants.
• The interdependence between plants and animals highlights the importance of plants in the ecosystem.

The density of air decreases with altitude, leading to a reduction in the amount of oxygen available for breathing. This makes it challenging for mountaineers to breathe at high altitudes. Therefore, they carry oxygen cylinders to ensure they have enough oxygen while climbing.

A wind vane is used to find the direction of the wind.
An anemometer is an instrument that measures wind speed and wind pressure
A barometer is a tool used to measure atmospheric pressure,

Carbon dioxide traps the sun's reflected rays that hit the earth's surface.

This leads to an increase in the earth's temperature, a phenomenon known as global warming.

• Carbon dioxide is a key greenhouse gas.
• It contributes to the greenhouse effect by retaining heat.
• Higher levels of carbon dioxide result in a warmer atmosphere.

Reducing carbon dioxide emissions is crucial for combating global warming.

The percentage of water vapour present in the air is called humidity.

Plants require nitrogen for their growth.

Nitrogen is essential for:

• Protein formation: It helps in building proteins, which are vital for plant structure and function.
• Cell growth: Nitrogen contributes to the development of new cells.
• Overall health: Adequate nitrogen levels ensure plants remain healthy and productive.

In summary, nitrogen is crucial for the growth and development of plants.

The percentage of nitrogen in the air is 78%.

• The atmosphere consists mainly of nitrogen and oxygen.
• Nitrogen makes up approximately 78% of the air we breathe.
• This high percentage is crucial for various environmental processes.

If we breathe air through our mouth, dust particles can enter our lungs and cause harm. In contrast, breathing through the nose is more hygienic because:

• The hair inside the nose acts as a filter, trapping dust particles.
• The mucus in the nose helps to trap and remove harmful particles.
• This process protects the lungs from potential irritants and infections.

Therefore, using the nose for breathing is a healthier choice.

When a straw is used for drinking, air is expelled from the straw, leading to a decrease in air pressure inside it.

This process allows the liquid in the container to:

• Enter the straw
• Rise up
• Come out of the straw

As a result, we can drink the liquid. When we stop using the straw, this process halts.

Humidity varies over time and between locations. It is not a constant value because it is influenced by the temperature of a specific area at any given moment.

• Humidity levels can change throughout the day.
• Different places experience varying humidity due to local climate conditions.
• Factors such as weather and geography play a significant role in these variations.

Carbon dioxide (CO₂) is commonly used in fire extinguishers because it displaces oxygen, thereby starving the fire of a key element needed for combustion. It is particularly effective on:

• Electrical fires
• Fires involving flammable liquids

The correct ascending order of gases based on their composition in air is:

• hydrogen < oxygen < nitrogen

In summary:

• Air primarily consists of nitrogen and oxygen.
• These two gases make up about 99% of the air.
• The remaining 1% includes carbon dioxide and other gases.

Air is useful in many ways:

• Generating electricity: Air movement can power windmills.
• Dispersing seeds: Wind helps spread seeds and pollen from plants.
• Birds' flight: Air is essential for birds, bats, and insects to fly.

Overall, air plays a crucial role in various natural processes and activities.

Hydrogen is a combustible gas. It burns with a pale blue flame, making it a key fuel source. Here are some important points about hydrogen:

• Combustibility: Hydrogen readily ignites and burns in the presence of oxygen.
• Flame Characteristics: It produces a pale blue flame, which is often difficult to see in daylight.
• Applications: Used in various industries, including fuel cells and rocket propulsion.

In summary, hydrogen is a highly flammable gas that plays a significant role in energy production.

Air is transparent and does not conduct electricity or heat well. Its composition varies from place to place.

• Air mainly consists of nitrogen and oxygen, which together make up 99% of its composition.
• The remaining 1% includes carbon dioxide, water vapour, and other gases.
• Air is present in all environments, including water and soil.
• Oxygen is essential for the survival of living organisms and supports combustion.
• The layer of air surrounding the Earth is known as the atmosphere, which is crucial for life.

The correct combination is a - 4, b - 3, c - 2, d - 1
(i) Aquatic animals-Dissolved oxygen
(ii) Mountaineers-Oxygen cylinders
(iii) Factories-Soot and dust
(iv) Wind-Sail boat

Rusting is an oxidation reaction where iron reacts with oxygen in the presence of water (moisture) to form iron oxide (rust). Oxygen is essential for this chemical change.