Test: Air - Class 7 MCQ

Answer: C) Atmosphere

The stratosphere is indeed almost free from clouds and is considered ideal for flying aeroplanes. This layer also contains a protective layer of ozone gas, which shields us from harmful sun rays. This absence of clouds and associated weather phenomena makes it safer for aircraft to travel without encountering turbulent weather conditions.

Air pressure is highest at sea level because the column of air above us is tallest, thus exerting the maximum pressure. As we ascend in altitude, the height of the air column decreases, resulting in a reduction in air pressure. Therefore, as we move away from sea level and ascend to higher elevations, the air pressure progressively diminishes. This principle explains why air pressure is greatest at sea level and decreases with increasing altitude.

• The thermosphere layer of the Atmosphere helps in Radio Transmission.
• It is located above the mesosphere and below the exosphere.
• In the thermosphere, the temperature rises rapidly with increasing height.
• The ionosphere is a part of this layer. 
• This layer helps in radio transmission and in fact, radio waves transmitted from the earth are reflected back to the earth by this layer.
• This layer is home to the International Space Station as it orbits Earth.

Weather refers to the short-term conditions of the atmosphere at a specific time and place. It includes factors such as temperature, humidity, wind speed, precipitation (rain, snow, etc.), and atmospheric pressure. Weather can change rapidly over minutes, hours, or days.

For example, weather describes if it is sunny, cloudy, raining, or snowing today. It focuses on immediate, day-to-day atmospheric conditions.

In contrast:

• Climate refers to the long-term average of weather patterns over a period of time (usually 30 years or more) in a specific region.
• Humidity is the amount of moisture or water vapor in the air.
• Precipitation refers to any form of water that falls from clouds, such as rain, snow, sleet, or hail.

Thus, weather is the correct term for the short-term state of the atmosphere.

• The temperature of the atmosphere does not stay the same throughout the year. It changes from season to season.
• In summers, it is hotter, while in winters, it is colder.
• This change happens because of the sun's energy that warms the Earth.
• The amount of sun's energy is different at different places on Earth, which is why some places are hotter than others.
• So, the temperature of the atmosphere changes, making the statement False.

Cold air is denser and heavy than warm air. The molecules are packed closer together. The amount of water vapor in the air also affects the density of the air. The more water vapor that is in the air, the less dense the air becomes. That is why cold, dry air is much heavier than warm, humid air.

The ozone layer is located in the stratosphere and plays a crucial role in shielding the Earth from the sun's harmful ultraviolet rays.

Troposphere: It is the most important layer of the atmosphere. The air we breathe exists here. It has the following features:

• Its average height is 13 km.
• Almost all the weather phenomena occur in this layer. The weather phenomena include: Rainfall, Fog, Hailstorm etc.

In the air we breathe, the most plentiful gas is nitrogen. It's important for plants to grow and for us to breathe. Nitrogen helps plants and animals to live. Hydrogen has least composition in air.