An amalgam is an alloy of mercury with another metal. For example, sodium amalgam (used as reducing agent), zinc amalgam (for Clemmensen reduction), and dental amalgam (mercury-silver-tin-copper). Most metals dissolve in mercury, forming amalgams, except iron and platinum. Amalgams can be liquid or solid depending on proportion. Used in gold extraction.
Explanation:
Sodium displaces hydrogen from water, a single displacement reaction. It is also a redox reaction (Na oxidized, H⁺ reduced). Not combination (one product), not decomposition (one reactant), not double displacement.
Explanation:
J.J. Thomson proposed the 'plum pudding' model (also called watermelon model) where the atom was considered a sphere of positive charge with electrons embedded like seeds. Rutherford's gold foil experiment disproved this by showing a dense, positively charged nucleus. Dalton proposed the indivisible atom theory. Bohr gave the model with discrete energy levels. Thomson discovered the electron but couldn't explain the nucleus.
Explanation:
Permanent hardness is due to dissolved sulfates and chlorides of calcium and magnesium. Boiling does not remove it. It requires chemical treatment (washing soda, ion exchange) or distillation. Temporary hardness (bicarbonates) is removed by boiling.
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