What is the formula for magnesium iodide?

The formula for magnesium iodide can be determined by following these steps:

### Step 1: Identify the ions involved
- **Magnesium (Mg)** belongs to Group 2 of the periodic table and thus forms a **Mg²⁺** ion (it loses two electrons to achieve a stable electron configuration).
- **Iodine (I)** belongs to Group 17 (halogens) and forms an **I⁻** ion (it gains one electron to achieve a stable electron configuration).

### Step 2: Balance the charges
To form a neutral compound, the total positive charge from magnesium must balance the total negative charge from iodine:
- Magnesium ion has a charge of **+2** (Mg²⁺).
- Iodine ion has a charge of **-1** (I⁻).

To balance the charges, you need **two iodide ions (I⁻)** to balance the **+2 charge** from one magnesium ion.

### Step 3: Write the formula
The formula for magnesium iodide is:
\[
\text{MgI}_2
\]
This indicates that one magnesium ion (Mg²⁺) is combined with two iodide ions (I⁻) to form a neutral compound.

### Final Answer:
The formula for magnesium iodide is **MgI₂**.