The electron geometry of sulfur dioxide (SO₂) involves two bond pairs and one lone pair around the sulfur atom. This geometry leads to a bent or V-shaped molecular structure, but when discussing electron geometry, we consider all electron groups (bonding and lone pairs).
Since there are three regions of electron density (two double bonds with oxygen and one lone pair), the appropriate prefix for the electron geometry would be "tri-".
Therefore, the answer is Tri-.