Final answer:
The unknown gas in the atomic spectra lab is likely argon, based on the given calculated molar mass. Atomic spectra are used to identify different gases, as each gas emits a unique pattern of colors related to its composition.
Step-by-step explanation:
Identifying the unknown gas in the atomic spectra lab involves analyzing the atomic spectra and physical properties of the gas. The given molar mass of 33.9 g/mol narrows down the possibilities, suggesting that the unknown gas could likely be argon, which has a close atomic mass of 39.948 g/mol as listed in the periodic table. Additionally, it's important to consider other possible gases like CH4 which also matches the estimated molar mass. Through the study of atomic spectra, it was discovered that different gases emit distinctive patterns of colors when heated or when a light is shined through them, which can be unique to each element or compound. For example, hydrogen emits one pattern of colors, sodium emits another, and a mixture would show both sets of colors. This property allows for the identification of the elements present in a gas sample.