Which pure substance can be classified as an element?
A chemical element is a pure substance that consists of only one type of atom. A chemical compound, on the other hand, is a substance formed when two or more different types of elements are chemically combined. To identify the element, we must examine the chemical composition of each given substance:
Comparing the components of each substance, we see that \(H_2\) is the only one composed of a single type of atom. Therefore, \(H_2\) is the only element in the list. The other substances—\(NO_3\), NaCl, and \(H_2SO_4\)—all contain at least two different types of elements, classifying them as compounds. The correct classification for the element is \(\boxed{H_2}\).
Understanding whether a substance is an element or a compound is fundamental to chemistry, as it helps determine the reactivity and properties of materials. For instance, knowing that pure oxygen (\(O_2\)) is an element is essential for understanding combustion and respiration, whereas knowing that carbon dioxide (\(CO_2\)) is a compound explains its different behaviors in firefighting and climate science. By identifying these building blocks, scientists can predict how different substances will behave when mixed or heated in industrial and laboratory settings.