Ice (solid H₂O) is a molecular solid where molecules are held together by hydrogen bonds and van der Waals forces. Diamond is a covalent network solid. NaCl is ionic solid. Iron is metallic solid. Molecular solids have low melting points, are soft, and are poor conductors. Other examples: dry ice (CO₂), iodine, sugar.
Explanation:
There are three naturally occurring radioactive decay series: the Uranium series (4n+2), the Thorium series (4n), and the Actinium series (4n+3). The Neptunium series (4n+1) is an artificial series; its longest-lived isotope, Neptunium-237, has a half-life too short to have survived since the Earth's formation.
Explanation:
Hydrogen has about 150 kJ/g (highest). Petrol ~47 kJ/g, coal ~25-35 kJ/g, cow dung cake ~8 kJ/g. Hydrogen produces only water on combustion and is a clean fuel.
Explanation:
Sublimation is the direct transition from solid to gas phase. Examples: naphthalene, camphor, iodine, solid CO₂ (dry ice). Evaporation is liquid to gas; condensation is gas to liquid; distillation separates liquid mixtures based on boiling points.
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