NCERT Solutions For Class 7 Social Science Our Environment Chapter 4 Air - 2025-26

To answer this question correctly according to the CBSE 2025-26 pattern, the NCERT solutions guide students to list the five layers of the atmosphere in order starting from the Earth's surface:

• Troposphere: The lowest and most important layer, where all weather phenomena like rainfall and fog occur.
• Stratosphere: Located above the troposphere, this layer contains the ozone layer, which protects us from the sun's harmful ultraviolet rays.
• Mesosphere: The third layer, where meteorites burn up upon entering from space.
• Thermosphere: In this layer, the temperature rises very rapidly with increasing height. It contains the ionosphere, which helps in radio transmission.
• Exosphere: The uppermost and thinnest layer, where light gases like helium and hydrogen float into space.

The NCERT Solutions for Chapter 4 clarify the distinction by defining each term based on time scale. Weather is the short-term, hour-to-hour or day-to-day condition of the atmosphere. For example, a hot or humid day refers to the weather. In contrast, climate is the average weather condition of a place over a much longer period, typically 25 years or more. For example, India has a monsoon climate.

The NCERT solutions provide a step-by-step reasoning process to answer this. First, state that humidity is the amount of water vapour in the air. Second, explain that on a humid day, the air is already full of water vapour, reaching its saturation point. Third, conclude that because the air cannot hold much more moisture, the rate of evaporation from the wet clothes slows down significantly, causing them to take longer to dry.

The NCERT Solutions for Class 7 Geography Chapter 4 outline the correct way to define the three mechanisms of rainfall:

• Convectional Rainfall: Occurs when the sun heats the ground, causing the air above it to become hot and rise. As it rises, it cools, condenses, and forms clouds, leading to heavy rainfall, often with thunder and lightning.
• Orographic Rainfall: Happens when moisture-laden wind is forced to move up a mountain barrier. As the air rises, it cools and condenses, causing precipitation on the windward side of the mountain.
• Cyclonic Rainfall: Associated with cyclones or depressions, this rainfall occurs when warm air and cold air meet. The warmer, lighter air is forced to rise over the colder, denser air, leading to condensation and precipitation over a large area.

It is crucial to list the atmospheric layers in the correct order (Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere) because this order reflects their altitude and distinct functions relative to the Earth's surface. The NCERT solutions present them this way to show a logical progression of changing temperature, pressure, and phenomena. An incorrect order would show a fundamental misunderstanding of the atmosphere's structure, which is a key concept in Chapter 4.

This concept is the core reason. The NCERT solutions link decreasing air pressure at high altitudes to a decrease in air density. This means there are fewer oxygen molecules in a given volume of air. Therefore, when solving this question, you must explain that mountaineers carry oxygen cylinders to supplement the low availability of oxygen in the thin air, which is essential for breathing and to avoid altitude sickness.

The NCERT solutions establish a direct cause-and-effect relationship that is fundamental to solving problems about wind. The core principle is that wind is simply the movement of air from high-pressure areas to low-pressure areas. Understanding this helps explain various phenomena, such as why sea breezes and land breezes occur or how large-scale wind patterns are formed across the globe. Correctly applying this principle is key to a high-scoring answer.

For a comprehensive answer on global warming as per the NCERT guidelines, you must include these points:

• The primary cause is the increase of greenhouse gases, especially carbon dioxide (CO₂), from human activities like burning fossil fuels.
• Explain the greenhouse effect: these gases trap heat radiated from the Earth, preventing it from escaping into space.
• Mention the consequence: this trapped heat leads to a gradual increase in the Earth's average temperature, which disrupts weather patterns and melts ice caps.

Including these three points demonstrates a full understanding of the topic.

A high-quality answer, as guided by the NCERT solutions, goes beyond just stating the percentages. It requires explaining their functional importance. For Nitrogen, the key significance is its role in plant growth through nitrogen fixation by soil bacteria, as plants cannot use it directly from the air. For Oxygen, the critical significance is its necessity for respiration in humans and animals, and its role in combustion. Explaining this ‘why’ demonstrates a deeper, more scientific understanding of the atmosphere's composition.