In which energy levels does carbon have electrons?

Carbon has a total of six electrons, and its electron configuration can be described in terms of energy levels. The first energy level can hold up to two electrons, and since carbon has a total of six electrons, the first energy level is filled with those two electrons. The remaining four electrons must occupy the second energy level. Therefore, in carbon's case, there are two electrons in the first energy level and four electrons in the second energy level.

This matches the correct choice, which states that carbon has 2 electrons in the first energy level and 4 in the second level. Understanding the concept of electron configuration is key to recognizing how many electrons reside within each energy level for any element, not just carbon.