Which of the following is true about an element?

An element is defined as a pure substance that consists of only one type of atom. Each element is characterized by its atomic number, which is the number of protons in its nucleus. This unique property means that elements cannot be broken down into simpler substances through chemical means. They can exist in various forms, such as solids, liquids, or gases, but they remain as a single type of atom throughout.

In contrast, a combination of different elements would describe a compound rather than an element itself. Moreover, elements can exist independently and do not have to be part of a compound; they can be found as monoatomic gases like noble gases (e.g., helium, argon) or as solid forms like metals (e.g., iron, gold). Thus, the statement emphasizing that an element contains only one type of atom accurately captures the essential characteristic that defines what an element is.