Answer:
3-
Step-by-step explanation:
Sodium aurothiosulfate is a salt with the formula Na₃Au(S₂O₃)₂. The cation of the salt is sodium ion, and the anion is aurothiosulfate ion. We can determine the charge of the aurothiosulfate ion, considering that the sum of the positive and negative charges must be equal to the charge of the compound, which is zero.
3 × Na⁺ + 1 × Au(S₂O₃)₂ⁿ⁻ = 0
3 × +1 + 1 × Au(S₂O₃)₂ⁿ⁻ = 0
Au(S₂O₃)₂ⁿ⁻ = 3-