Which compound is commonly known as nitrogen monoxide?

Nitrogen monoxide, commonly referred to as nitric oxide, has the chemical formula NO. This designation highlights that the compound consists of one nitrogen atom and one oxygen atom. In the context of nomenclature, systematic naming conventions dictate that the name reflects the elements involved and their respective quantities in the formula.

NO is a significant molecule in various chemical processes, particularly in biological systems, where it acts as a signaling molecule. Its importance extends to atmospherical chemistry and has implications in pollution and environmental science. On the other hand, the other options represent different compounds with distinct identities: N2O5 is dinitrogen pentoxide, CO is carbon monoxide, and SO2 is sulfur dioxide. Each of these compounds has a different composition and properties, thereby confirming that NO is specifically the only correct designation for nitrogen monoxide.