Nоte: 3-pаrt questiоn аt the end оf the reаding. Helium is primarily extracted as a byproduct of natural gas production. Helium accumulates underground over billions of years from the alpha decay of radioactive elements (uranium and thorium) in Earth's crust. It becomes trapped in natural gas reservoirs alongside methane. Extraction Process: 1. Crude natural gas is extracted from wells — helium content is typically 0.3–2.7% by volume (most of crude natural gas is methane). Natural gas is colorless and exists as a single, well-mixed gas phase with uniform composition throughout, even though its exact composition varies by reservoir. 2. Crude helium separation — the natural gas stream is cooled and compressed; methane and other hydrocarbons are liquefied and removed, leaving a crude helium stream (~50–70% He). 3. Purification — the crude helium is further purified via pressure swing adsorption (PSA) or cryogenic distillation to reach 100% purity. Unlike most gases, helium is light enough to escape Earth's atmosphere permanently once released — it's non-renewable on a human timescale. This is why scientists argue against using it for party balloons. Fill out the blanks below: Natural gas is classified as [mix1]. Methane has a formula of CH4 is classified as [mix2]. Once helium is sold in tanks as "100% helium" it is classified as [mix3].