SiO2 is a neutral molecule, so the sum of the oxidation numbers of all the atoms in the molecule must equal zero.

Here's how to determine the oxidation number of silicon (Si) in SiO2:

* Oxygen (O) typically has an oxidation number of -2.

* There are two oxygen atoms in SiO2.

* Let x be the oxidation number of silicon.

Therefore, the equation for the sum of oxidation numbers is:

x + 2(-2) = 0

Solving for x:

x - 4 = 0

x = +4

So, the oxidation number of silicon (Si) in SiO2 is +4.