Identify the correct formula for nickel(II) sulfate.

Nickel(II) sulfate is composed of nickel ions with a +2 charge and sulfate ions, which have a -2 charge. The nomenclature "nickel(II)" indicates that nickel has a valency of +2 in this compound. Sulfate, represented by the formula SO₄²⁻, carries a -2 charge.

When combining these ions to form the compound, one nickel ion will associate with one sulfate ion to balance the charges, leading to the formula NiSO₄. This formula reflects that there is one nickel ion and one sulfate ion in the compound.

In examining the other options, NiSO₂ suggests a different stoichiometry that does not reflect the charge balance for nickel(II) and sulfate. Ni2SO4 suggests two nickel ions, which would require a different balancing with sulfate not aligned with the +2 and -2 charges. Lastly, Ni(SO₄)2 implies that there would be two sulfate ions for every nickel ion, which describes nickel(IV) sulfate instead, not nickel(II) sulfate. Therefore, the correct formula for nickel(II) sulfate is NiSO₄.