Answer
Potassium Hydroxide - $KOH$
Work Step by Step
1. To begin, write the name of the first element with its charge. (Potassium has a charge of $^{+1}$ because its in Group 1) K$^{+}$
2. Then write the name of the second element with its charge. (Note - Hydroxide is a poly-atomic ion so, you have to remember its charge.) OH$_{-}$
3. Cross down the charges on both of the elements (+1 and -1) to get:
$$KOH$$