The correct answer to this question is D, potassium oxide. This is the correct name because Potassium (the K) is a metal with one valence electron while Oxygen (the O) is a nonmetal with two valence electrons. Thus, K2O is the ionic compound that is composed of oxygen and potassium.
K2O is a pale yellow solid, is a very rarely encountered, is a immensely reactive compound, and is the simplest oxide of potassium. Even combining K2O with water cause a violent reaction. Sometimes fertilizers and cement include the K2O compound, which is often criticized as it is considered to be unsafe and harmful.