Here's why:

* Cupric ion refers to the copper ion with a +2 charge (Cu²⁺).

* Tartrate is a negatively charged anion derived from tartaric acid.

* The compound copper tartrate is formed by the combination of cupric ions and tartrate anions.

The overall charge of the compound must be neutral. Therefore, the cupric ion must have a +2 charge to balance the negative charge of the tartrate anion.