CBSE Questions for Class 9 Biology Natural Resources Quiz 8 - MCQExams.com

• Humus is good for plant growth because it is formed by the decay of living organisms and is rich in nutrients. 
• Humus is a major factor in determining the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground.

• The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet (UV) radiation. 
• It contains high concentrations of ozone (O$$_3$$) in relation to other parts of the atmosphere.

• When you exhale when it's cold outside, the water vapour in your breath condenses into lots of tiny droplets of liquid water and ice (solid water) that you can see in the air as a cloud, similar to fog which appears smoke like. This process is called condensation.
• Hence Condensation process is responsible for the smoke-like vapour which comes out of the mouth in winter.
• So, the correct answer is 'Condensation'.

• Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase.
• By the process of evaporation, the water vapour enters into the air to form clouds in the sky. 
• The water vapour in the air condenses to form tiny water droplets which are the basis of clouds.
• Hence the process by which water vapour enters into the air to form clouds in the sky is Evaporation.
• So, the correct answer is option B.

A. Ammonification – The formation of ammonia from the dead bodies of plants and animals by means of decay or decomposition is called Ammonification. Employing this process, nitrogen content in the soil increases.

B. Biological nitrogen fixation – Conversion of atmospheric nitrogen into nitrogenous compounds utilizing microorganisms is called Biological nitrogen fixation. With the help of this process, nitrogen content in the soil increases.

C.Denitrification – Conversion of nitrates or nitrites into atmospheric or gaseous nitrogen is called Denitrification. Employing this process, nitrogen content in the soil decreases.

D. Nitrification – formation of nitrates from ammonia is called Nitrification. Through this process, nitrogen content in the soil increases.