Explanation

• Freshwater is water that contains a very low amount of salt, typically less than 1% salinity.
• Examples of freshwater sources include rivers, lakes, streams, and underground aquifers.

Last verified on 28-10-2026

Explanation

• Starlight passes through Earth’s atmosphere.
• Different air layers have different densities and temperatures.
• Light is repeatedly refracted (bent).
• This causes the star’s brightness to appear to change rapidly.
• This apparent change is called twinkling (scintillation).

Last verified on 26-10-2026

Explanation

• The ozone layer protects the Earth from the sun.
• It is a part of the atmosphere that absorbs most of the harmful ultraviolet light from the sun.
• It sits in the stratosphere.
• It is about 9 to 18 miles above the Earth.
• It stops dangerous UV rays from hurting living things.

Last updated by NS on 14-8-2026

Explanation

• A composite liner acts as a barrier that reduces the movement of contaminated liquid into the surrounding soil and groundwater.
• A leachate collection system collects polluted liquid produced when water passes through waste, allowing it to be treated safely.
• Methane capture collects gas released during the decomposition of biodegradable waste.
• Methane is a powerful greenhouse gas that contributes to global warming.
• Captured methane can be flared or used to generate energy, reducing its direct release into the atmosphere.

Last verified on 21-10-2026

Explanation

• Nitrogen (N₂) makes up about 78% of Earth's atmosphere. 
• It is generally not considered an air pollutant in its normal form.

Additional information:

• Hydrocarbons can contribute to air pollution by reacting with nitrogen oxides to form ground-level ozone.
• Chromium, especially certain compounds such as hexavalent chromium, can pollute the air and pose serious health risks.
• Carbon dioxide (CO₂) is a greenhouse gas that contributes to global warming and is also classified as an air pollutant in some environmental frameworks.

Last verified on 21-10-2026