Which one of the following is a monotomic element?

A monatomic element is one that exists naturally as a single atom rather than in molecular form. Noble gases are the primary examples of monatomic elements because they have completely filled valence shells, making them chemically stable and unlikely to bond with other atoms [1]. Helium (He) is explicitly identified as a monatomic noble gas [1]. In contrast, iodine (I) is one of the seven diatomic elements, naturally existing as I2 molecules. While metals like copper (Cu) and barium (Ba) are often represented by their atomic symbols in chemical equations, they typically exist in metallic lattice structures rather than as isolated single atoms in their standard state. Therefore, helium is the most accurate example of a monatomic element among the given options.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.3 HOW DO METALS AND NON-METALS REA ALS REACT? > p. 47