The main source of chlorofluorocarbons (CFCs) in the atmosphere is:
A. Fertilizers
B. Refrigerants and aerosol propellants
C. Volcanoes
D. Automobile exhaust
Answer: Option B
Solution (By JKExamLibrary)
CFCs were widely used as refrigerants (Freon), propellants in aerosol sprays, foam blowing agents, and solvents. They are chemically stable in the troposphere, drift to the stratosphere where UV breaks them, releasing Cl atoms that destroy ozone. Automobiles emit CO₂, NOx. Volcanoes emit SO₂. Fertilizers lead to N₂O.
Explanation:
Atomic radius decreases across a period due to increasing nuclear charge. Sodium (Na) is the first element in period 3, thus it has the largest atomic radius. Argon (noble gas) has the smallest (though noble gas radii are van der Waals and larger than covalent, but still trend is decreasing). For metals, Na > Mg > Al; non-metals further smaller.
Explanation:
J.J. Thomson discovered the electron in 1897 using a cathode ray tube. He showed that cathode rays were composed of negatively charged particles (electrons) that were much lighter than atoms and were a fundamental part of all matter, leading to his plum pudding model.
Explanation:
Total electrons = 16 (Sulfur). Period = number of shells = 3. Valence electrons = 6, group = 10+6 = 16 (Group 16, chalcogens). Group 6 would be 6 valence electrons but in d-block, not applicable. Group 18 has 8 valence electrons (except He). So sulfur is in group 16, period 3.
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