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1: There is no calcium and magnesium ions in soft water, corrosion and rust will occur under the action of chloride ions, iron ions will corrode and rust under the action of oxygen ions, and trivalent iron ions and hydrogen molecules will be produced under the action of hydrogen ions to corrode and rust.
2: There are only water molecules in pure water, and trivalent iron ions and hydrogen molecules are generated under the action of hydrogen ions to corrode and rust, and iron ions are corroded and rusted under the action of oxygen ions.
3: Tap water only produces corrosion and rust under the action of iron ions and oxygen ions.