Which is the chemical formula for nickel(II) nitrate hexahydrate?

Nickel(II) is Ni²⁺, and nitrate is NO₃⁻, so two nitrate ions are needed to balance one nickel ion: Ni(NO₃)₂. “Hexahydrate” means six water molecules are attached, giving Ni(NO₃)₂•6H₂O. Therefore, the correct choice is C, Ni(NO₃)₂•6H₂O.

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