Final answer:
The upper flammable limit of methane is the highest concentration in air that is combustible; the exact value is not provided in the examples referenced.
Step-by-step explanation:
The question pertains to the upper flammable limit (UFL) of methane (CH4) in air. The UFL is a property used to characterize the flammability of gases and represents the highest concentration of the gas in air that will combust when exposed to a flame or ignition source. While the specific UFL value for methane is not provided in the examples, in general terms, methane's flammability in air highlights the need for correct handling and storage, especially when considering its use as an alternative fuel. Methane's tetrahedral geometry, with each of the four hydrogen atoms spaced 109.5° apart, might not directly relate to its UFL but is a characteristic of its molecular structure. As methane is a potent greenhouse gas, measures such as flaring at drill sites are sometimes used to prevent its release into the atmosphere.