The relative atomic mass of a triatomic element cannot be directly determined solely based on its density at STP (Standard Temperature and Pressure). The density of a substance is related to its molar mass and the packing of its atoms or molecules in a given volume. However, it does not provide direct information about the individual atomic masses.
To determine the relative atomic mass of a triatomic element, additional information is required. The relative atomic mass (also known as atomic weight) is determined through various experimental techniques, such as mass spectrometry, which measures the masses and relative abundances of isotopes.
Isotopes are atoms of the same element with different numbers of neutrons, resulting in different atomic masses. The relative atomic mass of an element is a weighted average of the atomic masses of its isotopes, considering their relative abundances.
Therefore, to determine the relative atomic mass of a triatomic element, you would need to consult reliable sources such as scientific literature, periodic tables, or databases that provide the atomic mass of that specific element based on experimental measurements. The density alone is insufficient to determine the relative atomic mass accurately.