2. Distortions do not always result only from the electronic structure. Sometimes the substituents have too much volume.
3. resonance delocalization is always associated with multiple bonds.
4. HI - for a linear diatomic molecule the angle is indeterminate (angle needs 3 points)
Carbonate anion - missing electrons in resonant structures (count electrons), also missing one resonant structure
Silicon dioxide - a linear triatomic molecule does not have a 109.5-degree angle, although in a crystal silicon atom is almost always surrounded by four oxygen atoms and then the angle is tetrahedral.