Final answer:
Nonmetal gases are typically composed of individual atoms or diatomic molecules and have low melting points, unlike extended structures with high melting points.
Step-by-step explanation:
The properties that describe elements that are nonmetal gases include being composed of individual atoms or diatomic molecules and having low melting points. Nonmetal gases are not composed of extended structures and do not typically have high melting points. For example, noble gases such as helium (He) and neon (Ne) exist as individual atoms, while gases like hydrogen (H2), nitrogen (N2), and oxygen (O2) are diatomic molecules.