3Ni2 + (aq) + 2Co (s) ⟶2Co3 + (aq) + 3Ni (s) Which substance gets oxidized?

Co⁰ - 3e⁻ → Co³⁺ (cobalt loses electrons so it is oxidized)

Explanation:

When a substance is oxidized it means that it loses electrons.

When a substance is reduced it means that it gains electrons.

Ni²⁺ + 2e⁻ → Ni⁰ (nickel gains electrons so it is reduced)

Co⁰ - 3e⁻ → Co³⁺ (cobalt loses electrons so it is oxidized)