The scientist who first proposed that electrons move in specific orbits around the nucleus was:
A. Niels Bohr
B. J. J. Thomson
C. Ernest Rutherford
D. James Chadwick
Answer: Option A
Solution (By JKExamLibrary)
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:
Hydrochloric acid (HCl) was historically called muriatic acid or spirits of salt, produced from salt (NaCl) and sulfuric acid. Oil of vitriol is H₂SO₄. Aqua regia is a mixture of 3 parts HCl and 1 part HNO₃. Carbolic acid is phenol. HCl is present in gastric juice and used in metal cleaning and chemical synthesis.
Explanation:
Dalton's atomic theory (1808) provided a framework for the laws of chemical combination—conservation of mass, constant composition, and multiple proportions. The law of multiple proportions states that when two elements form more than one compound, masses of one that combine with fixed mass of the other are in small whole number ratios. Dalton proposed atoms combine in simple whole number ratios to form compounds.
Explanation:
Graham's law: r₁/r₂ = √(M₂/M₁). Given rA/rB = 1/2, so √(MB/MA) = 1/2. Squaring: MB/MA = 1/4 => MB = MA/4 = 64/4 = 16 g/mol. B is lighter and diffuses faster. Logical check: rate inversely proportional to square root of molar mass; if rate is double, mass is quarter. Answer is 16.
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