Answer
$Sc_{2}S_{3}$
Work Step by Step
When a compound is formed, the overall charge must be neutral. Scandium, the problem states, has a charge of +3. In order to get the electron configuration of the nearest noble gas, Argon, Sulfur must gain two electron, making the charge of a Sulfur ion -2. The overall charge of the compound must be neutral, so the overall charges of both ions must cancel out. Looking for the least common factor of 2 and 3, it becomes clear that all of the Scandium ions must together have a charge of +6 while all of the Sulfur ions must combine to have a charge of +6. Hence, there must be 3 Sulfur ions and 2 Scandium ions, making the compound $Sc_{2}S_{3}$.
