Which of the following gases is responsible for the depletion of the ozone layer?
A. Chlorofluorocarbons (CFCs)
B. Carbon dioxide
C. Sulfur dioxide
D. Methane
Answer: Option A
Solution (By JKExamLibrary)
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.
Explanation:
Oxygen (atomic number 8) has electronic configuration 2,6. It needs 2 more electrons to complete its octet. In water (H₂O), it shares two electrons (one each with two hydrogen atoms), forming two covalent bonds. Hence valency = 2. Oxidation number is -2.
Explanation:
Temporary hardness is due to dissolved bicarbonates of Ca and Mg. These can be removed by boiling, which precipitates carbonates. Calcium sulfate and chloride cause permanent hardness. Sodium chloride does not cause hardness. Boiling: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Bicarbonates are formed when water containing CO₂ passes over limestone.
Explanation:
The 'lock-and-key' model explains enzyme specificity: the substrate fits into the active site like a key in a lock. Protein nature is general; specificity arises from 3D structure.
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