Which of the following metals is used in the thermite welding process? MCQ with Answer and Explanation

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:
Hydrogenation of alkenes (addition of H₂ across double bond) is catalyzed by finely divided metals like nickel, platinum, or palladium. These adsorb H₂ and the unsaturated compound, facilitating reaction. V₂O₅ is for oxidation (Contact), MnO₂ for H₂O₂ decomposition, Fe for Haber process. Nickel is the most common industrial catalyst for hydrogenation.

Explanation:
Hard water contains dissolved Ca²⁺ and Mg²⁺ ions which react with soap to form insoluble scum, preventing lather. Soft water lathers readily. Distilled water is pure (soft). Rainwater is naturally soft but may dissolve CO₂ and become slightly acidic.