What volume of 12.0M KCl is required to make 300.0 ml of 0.50 M KCl?

In order to make 300.0 ml of 0.50 M KCl you need 0.300 L x 0.50 M = 0.150 moles KCl. To make 0.150 moles of 12.0 M KCl you need 0.150 moles / 12.0 M = 0.0125 L = 12.5 ml.