The formula for Iron(III) dihydrogen phosphate is Fe(H₂PO₄)₃. Here's how to break it down:

* Fe: The symbol for Iron.

* (III): This Roman numeral indicates the Iron ion has a +3 charge (Fe³⁺).

* H₂PO₄: The dihydrogen phosphate ion, which has a -1 charge.

* ₃: This subscript indicates that there are three dihydrogen phosphate ions for every iron ion.

Therefore, the complete formula is Fe(H₂PO₄)₃.