What evidence do you have for the following statements? a) zinc chloride is a pure substance not a mixture b) water is a pure substance

a) A compound is a pure substance because its molecule cannot be broken down into simpler particles by physical means.

Pure substance is made of only one type of atom (element) or only one type of molecule, it has definite and constant composition with distinct chemical properties.

Pure substances can be separated chemically, not physically, that is difference between pure substances and mixtures.

b) Water can be separated only by chemical means,

Electrolysis of water is the decomposition reaction, because from one molecule (water) two molecules (hydrogen and oxygen) are produced. Water is separeted into two molecules:

Reaction of reduction at cathode: 2H⁺(aq) + 2e⁻ → H₂(g).

Reaction of oxidation at anode: 2H₂O(l) → O₂(g) + 4H⁺(aq) + 4e⁻.

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i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)