Oxygen (atomic number 8) has electronic configuration 2,6. It needs 2 more electrons to complete its octet. In water (H₂O), it shares two electrons (one each with two hydrogen atoms), forming two covalent bonds. Hence valency = 2. Oxidation number is -2.
Explanation:
Saline water (containing NaCl) increases the electrical conductivity of the water, accelerating the electrochemical process of rusting. This is why ships and coastal structures rust faster. Dry air and vacuum have no moisture; pure water without dissolved oxygen slows rusting.
Explanation:
Marble is primarily calcium carbonate (CaCO₃). It reacts with acid rain (containing H₂SO₄ and HNO₃) to form soluble salts, causing erosion: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. This is why monuments like Taj Mahal are affected. CaCO₃ is basic, so it neutralizes acid. Restoration and pollution control are needed to protect heritage.
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