The main impurity present in iron ore obtained from mining is: MCQ with Answer and Explanation

Explanation:
SO₂ (from burning coal) and NOₓ dissolve in rain to form H₂SO₄ and HNO₃. CO is toxic but does not form strong acid; CH₄ is greenhouse gas; ground-level O₃ is secondary pollutant and irritant.

Explanation:
Natural gas is primarily methane (CH₄), typically 70-90%, along with small amounts of ethane, propane, butane, and other hydrocarbons. It is a fossil fuel formed from the remains of ancient marine organisms. CNG (compressed natural gas) is methane stored at high pressure. LPG (liquefied petroleum gas) mainly contains propane and butane. Methane has the highest calorific value among the given options per unit mass.

Explanation:
Eutrophication is the excessive richness of nutrients (mainly nitrates and phosphates from fertilizers and sewage) in a lake or other body of water. This causes a dense growth of plant life (algal blooms) and depletion of oxygen, killing aquatic animals and disrupting the ecosystem.