Here's how to determine the ionic compound formed by Radium (Ra) and Sulfur (S):

* Identify the charges:

* Radium (Ra) is in Group 2, so it forms a +2 ion (Ra²⁺).

* Sulfur (S) is in Group 16, so it forms a -2 ion (S²⁻).

* Balance the charges: The charges are already balanced (2+ and 2-).

* Write the formula: Since the charges are equal and opposite, the formula is simply RaS.

Therefore, the ionic compound formed by Radium and Sulfur is RaS, which is called Radium Sulfide.