Which of the following is NOT a method of concentration of ore?
A. Leaching
B. Magnetic separation
C. Froth flotation
D. Smelting
Answer: Option D
Solution (By JKExamLibrary)
Smelting is a reduction process, not concentration. Concentration (beneficiation) methods include gravity separation, magnetic separation, froth flotation, and leaching (chemical). Smelting involves heating concentrated ore with a reducing agent to extract metal. For example, hematite concentrated by washing, then smelted in blast furnace.
Explanation:
Evaporation of water is a physical change—liquid water changes to water vapor, but the chemical composition (H₂O) remains unchanged. Souring of milk and curd formation involve lactic acid bacteria converting lactose to lactic acid (chemical change). Fermentation of grapes involves yeast converting sugars to ethanol and CO₂. Chemical changes produce new substances. Physical changes only alter the state or form.
Explanation:
Ernest Rutherford discovered the atomic nucleus through his gold foil experiment (1911). J.J. Thomson discovered the electron (1897). Chadwick discovered the neutron (1932). Bohr proposed the model of the atom with quantized energy levels (1913), not the electron. Rutherford also discovered the proton (1919). Naming discoveries correctly is important for competitive exams.
Explanation:
Mendeleev named the missing element eka-aluminium. When gallium was discovered (1875), its properties (density, oxide formula) closely matched Mendeleev's predictions, validating his table. Germanium was eka-silicon; scandium was eka-boron. These predictions were a triumph of the periodic law. Gallium has a low melting point (~30°C) and is used in semiconductors. Mendeleev corrected atomic masses based on group properties.
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