What is commonly stored in a spherical container?

Spherical containers are specifically designed to handle gases and liquids under pressure, and they are most commonly used for substances that require high structural integrity and low surface area to volume ratios. Methane, being a gas at ambient temperatures and pressures, is stored in spherical containers mainly because this shape can effectively manage the pressure of the gas. The shape minimizes the stress on the container walls, allowing for safe storage and minimizing the risk of rupture.

Spherical containers are also beneficial for transporting gases like methane, as they help maintain a consistent pressure and facilitate efficient filling and emptying processes. This storage method is not as suitable for liquids like methanol or butane under normal conditions, since they can be stored in cylindrical tanks or other shapes without the same critical pressure considerations. In the case of propylene, while it may also be stored in various types of containers, it is typically handled in different forms depending on its state and required storage conditions. Thus, methane is the most appropriate answer based on the characteristics and storage requirements of the substance.