The yellow stain on your kitchen floor is likely due to the rubber backing on the rug altering the finish on your flooring. You may not be able to remove the stain without stripping the wax and recoating the floor. Before getting that drastic, try making a baking soda paste, with baking soda and water, and applying it to the stain. Allow it to sit overnight, scrub and rinse. You could also try hydrogen peroxide on the stain, or a weak bleach solution.