Here's why:

* Chromium (Cr) is a metal, and metals tend to lose electrons to form positively charged ions (cations).

* Sulfate (SO₄²⁻) is a polyatomic ion, meaning it's a group of atoms that act as a single unit with a negative charge.

Ionic bonds form when a metal loses electrons to a nonmetal (or polyatomic ion), creating oppositely charged ions that attract each other electrostatically.