"Trioxide" is not an element or a specific compound, but rather a suffix that indicates the presence of three oxygen atoms in a compound. To determine valency, we need to know the specific element or compound containing the trioxide.

For example:

* Sulfur trioxide (SO3): Sulfur has a valency of +6, while each oxygen has a valency of -2. Therefore, the valency of the sulfur in sulfur trioxide is +6.

* Chromium trioxide (CrO3): Chromium has a valency of +6, and each oxygen has a valency of -2. Therefore, the valency of the chromium in chromium trioxide is +6.

Please provide the specific compound containing the trioxide so that I can determine the valency.