Read the following passage concerning the discovery of argon:
In 1892, Lord Rayleigh observed a persistent discrepancy in the density of nitrogen gas depending on its provenance: nitrogen isolated from atmospheric air was consistently approximately 0.5 percent denser than nitrogen synthesized through the chemical decomposition of compounds such as ammonium nitrite. While some contemporary physicists posited that atmospheric nitrogen might contain allotropic triatomic nitrogen () molecules analogous to ozone, William Ramsay collaborated with Rayleigh to investigate whether the anomaly pointed to an uncharacterized, heavier atmospheric constituent. To evaluate this, they revisited Henry Cavendish's 1785 spark-discharge experiments, in which Cavendish had noted that after repeatedly sparking air with excess oxygen and absorbing the resulting nitrogen oxides, an unreactive gas bubble comprising roughly 1/120th of the initial volume remained unabsorbed. Replicating and scaling this selective removal of known reactive components, Rayleigh and Ramsay successfully isolated a dense, chemically inert gas. Subsequent acoustic measurements of the gas's specific heat ratio () demonstrated that its particles possessed only translational degrees of freedom, definitively proving the gas—named argon—to be monatomic rather than polyatomic.
Match each cited detail from the passage with the primary rhetorical function it serves in the author's account.
- nitrogen synthesized through the chemical decomposition of compounds such as ammonium nitriteServing as a standardized baseline control against which the anomalous mass of atmospheric samples was identified
- allotropic triatomic nitrogen () molecules analogous to ozoneRepresenting a competing hypothesis regarding the anomaly's source that required evaluation
- Cavendish's 1785 spark-discharge experimentsIdentifying an earlier empirical observation that foreshadowed the existence of an unreactive fraction
- acoustic measurements of the gas's specific heat ratio ()Supplying physical evidence that conclusively determined the single-atom structure of the isolated substance