What propelling charge is an individual, bi-directional charge, green in color, and has a center core igniter encased in a rigid combustible case?

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Propelling charges are designed to deliver a precise amount of propellant in a single unit with a specific ignition arrangement. An individual, bi-directional charge means you can insert it in either orientation in the cartridge and it will ignite reliably, which is important for certain weapon systems where orientation can vary during handling. The green color coding helps technicians quickly identify the charge type in the field. A center core igniter encased in a rigid combustible case indicates the igniter is built into the core and the whole assembly is protected by a solid casing to ensure controlled ignition and burn characteristics.

With these exact features—single-use, bi-directional compatibility, green designation, and a center-core igniter inside a rigid case—the charge described is M231. The other options do not meet all of these design traits.