Here's why:

* Reaction with bases: SiO₂ reacts with strong bases to form silicates. For example, it reacts with sodium hydroxide (NaOH) to form sodium silicate (Na₂SiO₃):

SiO₂ + 2NaOH → Na₂SiO₃ + H₂O

* Non-reaction with acids: SiO₂ is generally unreactive with acids, except for hydrofluoric acid (HF) which can dissolve it.

* Structure: The silicon atom in SiO₂ is surrounded by four oxygen atoms in a tetrahedral arrangement. This structure is similar to the structures of acidic oxides like CO₂ and SO₂.

Note: While SiO₂ itself is an acidic oxide, its properties can be influenced by its structure and the presence of impurities. For example, amorphous silica is less acidic than crystalline silica.