Here's how to determine the formula of the compound between Be and NO₂⁻:

1. Identify the charges:

* Beryllium (Be) has a +2 charge (Be²⁺).

* The nitrite ion (NO₂⁻) has a -1 charge.

2. Find the least common multiple (LCM) of the charges:

* The LCM of 2 and 1 is 2.

3. Determine the subscripts:

* To achieve a total charge of 0, you need one Be²⁺ ion (2+ charge) and two NO₂⁻ ions (2- charge).

4. Write the formula:

The formula of the compound is Be(NO₂)₂.