"Dioxide" is a suffix, not an element. It refers to a compound containing two oxygen atoms per molecule.

To figure out the element in a dioxide, you need to know the whole compound's name.

For example:

* Carbon dioxide (CO2) contains the element carbon.

* Silicon dioxide (SiO2) contains the element silicon.

* Nitrogen dioxide (NO2) contains the element nitrogen.

Let me know if you have a specific dioxide in mind, and I can tell you the element it contains!