An unknown substance is a white solid at room temperature and has a melting point of 78 °C. Which of the following substances is most likely to be the identity of the unknown sample? six white pellets A. Naphthalene, a molecular solid with the formula C10H8 B. Silica, a network solid held together by covalent bonds with the formula SiO2 C. Calcium chloride, an ionic compound with the formula CaCl2 D. Water, an molecular compound with the formula H2O