The white dwarf that remains when our Sun dies will be mostly made of ______.

The white dwarf that will remain after the Sun exhausts its nuclear fuel will primarily consist of carbon and oxygen. This occurs because the Sun, which is classified as a G-type main-sequence star, will undergo nuclear fusion throughout its life cycle, initially fusing hydrogen into helium in its core. Once hydrogen is depleted, the core contracts and the temperature rises, allowing the helium to fuse into carbon and oxygen during helium burning.

Eventually, the Sun will shed its outer layers and leave behind a core that is no longer undergoing fusion, which will result in the formation of a white dwarf. At this stage, the core primarily consisting of carbon and oxygen will be left, as these elements are the remnants of the fusion processes that occurred when the Sun was in the later phases of its lifecycle. Therefore, the correct answer emphasizes that the white dwarf predominantly contains carbon, as well as some oxygen, reflecting the fusion history of the star.