The scientist who first proposed that electrons move in specific orbits around the nucleus was:
A. J. J. Thomson
B. James Chadwick
C. Ernest Rutherford
D. Niels Bohr
Answer: Option D
Solution (By JKSSB Mock Tests)
Niels Bohr in 1913 proposed the planetary model where electrons revolve in certain allowed circular orbits without radiating energy, with quantized angular momentum. Rutherford proposed the nuclear model but did not specify quantized orbits. Thomson gave plum pudding. Chadwick discovered neutron.
Explanation:
(NH₄)₂SO₄ contains 21% nitrogen and 24% sulfur. Both are plant nutrients. It is a straight nitrogenous fertilizer with sulfur as secondary nutrient. It is especially useful for sulfur-deficient soils.
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.
Explanation:
Phenolphthalein is colorless in acidic and neutral solutions, turning pink/magenta in basic solutions with pH > about 8.2-10. It is commonly used in acid-base titrations. Methyl orange is red in acidic and yellow in basic. Litmus is purple in neutral, red in acid, blue in base. Natural indicators like turmeric, beetroot also show color changes.
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