What is defined as the arrangement of elements of a unit in a prescribed manner?

The correct term that defines the arrangement of elements of a unit in a prescribed manner is formation. In a military context, formation refers specifically to how troops or equipment are positioned in relation to one another to achieve tactical objectives. This can involve various shapes or configurations, depending on the mission requirements, terrain, and enemy positions.

Formation is fundamental to military strategy, as it affects how units can engage with the enemy, move on the battlefield, and maintain command and control. For example, formations can provide better coverage, enhance communication among units, or facilitate specific types of movements during an operation, such as an advance or a retreat.

The other terms do have relevance in different contexts but do not capture the specific military meaning associated with the organized positioning of units. Composition typically refers to the makeup or organization of a unit, layout pertains more to spatial arrangement, and order can imply sequence or command rather than spatial or organizational structure. Hence, formation is the most precise term for describing this concept within the military framework.