Here's why:

* Hydrogen (H): Hydrogen contributes one positive charge.

* Sulfur (S): Sulfur contributes six positive charges.

* Oxygen (O): Each oxygen atom contributes two negative charges. There are four oxygen atoms, resulting in a total of eight negative charges.

To balance the charges:

* 1 (H) + 6 (S) - 8 (O) = -1

This gives us a net negative charge of -1, resulting in the formula HSO₄⁻.