Calcium oxide, commonly known as lime, is a white powder. This coloration is due to the high concentration of calcium ions in its crystalline structure, which absorbs light across the visible spectrum, reflecting white light. The data supporting this is derived from various scientific studies that have analyzed the optical properties of calcium oxide. For instance, a study published in the Journal of Physical Chemistry B (2009) found that calcium oxide exhibits a white color due to its ability to scatter light effectively across the visible spectrum. Additionally, the reflectance spectrum of calcium oxide shows a peak in the blue region, which contributes to its overall white appearance.