Question

### Venusian Phosphine Debate

In 2020, researchers reported the detection of phosphine ($PH_3$) in the temperate cloud decks ($50–60\text{ km}$ above the surface) of Venus. Because $PH_3$ is rapidly destroyed by photolysis and oxidation in Venus's highly acidic atmosphere, any detectable level of $PH_3$ suggests a continuous source of production. Three hypotheses were proposed to explain the source of the detected $PH_3$.

Hypothesis 1 (Biotic Source)
The detected $PH_3$ is produced by anaerobic microbial life residing in the temperate cloud decks. In this environment, temperatures and pressures are relatively mild. Terrestrial anaerobic bacteria are known to produce $PH_3$ from phosphate minerals, and similar biochemical pathways must be active on Venus. Because thermodynamic calculations show that the abiotic production of $PH_3$ under Venus's atmospheric conditions is highly unfavorable, non-biological reactions cannot explain the observed concentration. Thus, biological activity is the only viable mechanism.

Hypothesis 2 (Volcanic Source)
Active volcanism on Venus is responsible for the phosphine. Eruptions eject phosphorus-bearing minerals, such as phosphides ($Fe_3P$), from the deep mantle into the lower atmosphere. As these minerals rise into the acidic cloud deck, they react with sulfuric acid ($H_2SO_4$) to form $PH_3$ gas. This abiotic mechanism does not require biological activity and can account for the observed $PH_3$ concentration, provided Venus is volcanically active. Abiotic photochemical models, however, are insufficient to produce $PH_3$.

Hypothesis 3 (Photochemical Source)
Atmospheric photochemistry driven by solar ultraviolet (UV) radiation synthesizes $PH_3$. Solar UV radiation initiates reactions in the upper atmosphere that reduce oxidized phosphorus compounds (like orthophosphoric acid) in the presence of trace hydrogen sources. While thermodynamic models suggest abiotic pathways are unfavorable in the bulk atmosphere, localized photochemical reactions near the cloud tops can generate the observed $PH_3$ abiotically.

Based on the descriptions of the three hypotheses, which hypothesis or group of hypotheses agrees with each statement regarding the production and behavior of Venusian phosphine? Match each statement on the left with the correct hypothesis or group of hypotheses on the right.