The formula Ni₂CO₃ is incorrect. Here's why and how to get the correct formula:

* Nickel (Ni) is a transition metal with a common charge of +2 (Ni²⁺).

* Carbonate (CO₃) is a polyatomic ion with a charge of -2 (CO₃²⁻).

To form a neutral compound, the charges must balance. Since the charges of nickel and carbonate are equal and opposite, they combine in a 1:1 ratio.

Therefore, the correct molecular formula for nickel carbonate is NiCO₃.