The process of converting a concentrated ore into its oxide by heating in excess air is:
A. Roasting
B. Smelting
C. Calcination
D. Refining
Answer: Option A
Solution (By JKSSB Mock Tests)
Roasting is the process of heating the concentrated ore (usually sulfide ores) strongly in the presence of excess air below its melting point. It converts the ore to its oxide form and removes volatile impurities as gases (e.g., 2ZnS + 3O₂ → 2ZnO + 2SO₂).
Explanation:
Temporary hardness is due to dissolved bicarbonates of Ca and Mg, which can be removed by boiling: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Permanent hardness is caused by chlorides and sulfates of Ca and Mg, not removed by boiling. Sodium bicarbonate does not cause hardness. Methods to remove permanent hardness include treatment with washing soda (Na₂CO₃), ion exchange, or calgon.
Explanation:
Carbon-14 dating is used to determine age of organic materials up to ~50,000 years based on its half-life of 5730 years. Cobalt-60 for cancer therapy, iodine-131 for thyroid, uranium-235 for nuclear fuel.
Explanation:
Chlorofluorocarbons (CFCs), once widely used as refrigerants and propellants, are the primary culprits behind ozone depletion. When CFCs reach the stratosphere, UV radiation breaks them down, releasing chlorine atoms. A single chlorine atom can catalytically destroy thousands of ozone (O3) molecules.
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