Soil is formed by breaking down of rocks at or near the surface of the Earth through various physical, chemical, and biological processes by various factors such as the sun, water, wind, and living organisms.→ Sun: During day time, the rocks are heated up by solar rays. This causes the rocks to expand. During night time, these rocks cool down and contracts, thus the cracks devlop in the rock and they break down.
→ Water: It helps in breaking of rocks in two ways:
(i) It goes into the cracks and crevices formed in the rocks. When this water freezes, its volume increases. As a result, the size of the cracks also increases. This helps in the weathering of rocks.
(ii) Water moving in fast speed carries big and small particles of rock downstream. These rocks rub against each other, resulting in breaking down of rocks.These smaller particles are carried away by running water and deposited down its path.→ Wind: Strong winds carry away rocks, which causes rubbing of rocks. This results in the breaking down of rocks into smaller and smaller particles.
→ Living Organism: Some living organisms like lichens help in the formation of soil. Lichens grow on rock surfaces and converts them into powdery form and make soil layer. In the same way, the plants like moss also help in the making of fine soil particles.

The blowing away or washing away of land surface bywind or water is known as soil erosion.

The methods of preventing or reducing soil erosion are:
→ Plantation of tress and plants→ Prevention of deforestation
→ Prevent excessive grazing

Water is found in three different states during the water cycle:
→ Solid (Snow, Ice)
→ Liquid Water (ground water, river water, etc.)
→ Gaseous State (Water vapours)

Two biologically important compounds that contain both oxygen and nitrogen are:
(i) Amino acids
(ii) Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)

Three Human activities are:

→ Burning of fuels in various processes like heating, cooking, transportation, and industry.
→ Human induced forest fires
→ The process of deforestation includes the cutting down of trees. This decreases the uptake of carbon dioxide for photosynthesis. Eventually, the content of carbon dioxide increases

Some gases like carbon dioxide, methane, nitrous oxide prevent the escape of heat from the Earth's surface by trapping it. This increases the average temperature of the Earth. This is called the green house effect. 

The two forms of oxygen found in the atmosphere are:
→ Diatomic molecular form with chemical formula O₂.
→ Triatomic molecular form with chemical formula O₃known as ozone.