Chapter 2 - Atoms, Molecules, and Ions - Exercises - Page 77: 2.61b

$K_{2}CO_{3}$

An ionic compound will always have a neutral charge. The problem states that Carbonate ($(CO_{3})$) has a charge of -2 while a Potassium (K+) ion will have a charge of +1. To cancel out the -2 charge of Carbonate, there must be two Potassium ions, hence making the ionic compound formed between these two ions $K_{2}(CO_{3})$.