Decoxide vs decaoxide?

Now, I know that this is more of a science question, but it’s more on the English-y side of science, so I’m here.

I’m doing a science worksheet and I came across an opportunity to write either "decoxide" or "decaoxide". Since the latter sounds wrong out loud, I decided to google it before I wrote it out, just to be sure. What I got instead, once I had filtered out all of the references to phosphorus or tetraphosphorus, was a whole lot of mentions of both. Both my phone’s autocorrect and my worksheet itself use "decoxide". So, I did the first thing I thought of and went to r/askscience. However, after I’d gotten no responses on there, I realized my mistake and came to Stack Exchange.

Update: How do you write "three iodine atoms"? Is it "triiodide" (which my autocorrect says is correct, and which Wikipedia apparently uses) or is it "triodide" (which my autocorrect approves of)? Or even "tri-iodide"?

Thanks for any help you guys can provide!