The formula for mercury(II) perchlorate is Hg(ClO₄)₂. Here's why:

* Mercury(II): This indicates that mercury has a +2 charge (Hg²⁺).

* Perchlorate: This is the polyatomic ion ClO₄⁻ with a -1 charge.

To balance the charges, you need two perchlorate ions for every one mercury(II) ion.