Especially since you mentioned your tank ruptured, those parts look very similar (although different) to the float and float guide shown clearly in this great thread:
https://xoutpost.com/983445-post3.html
Could be that the difference between your photos and those in that thread are due to OE vs. aftermarket.
Does the white thing float? Is that dark ring at one end magnetic?
If this theory is correct, you don't need to worry about anything - the replacements for those parts are already in the expansion tank you bought.