Which word best represents someone who is enthusiastic and energetic?

The word "alacrity" best represents someone who is enthusiastic and energetic. It specifically denotes a cheerful readiness, brisk and lively action or eagerness in response to something. When a person exhibits alacrity, they are not only willing to participate but do so with an energetic spirit that reflects enthusiasm.

In contrast, the other options do not convey the same sense of energetic eagerness. "Choleric," for instance, refers to a temperament characterized by anger or irritability rather than enthusiasm. "Replete" means filled or well-supplied with something but does not communicate any sense of energy or enthusiasm. "Volubility" indicates a tendency to talk a lot or fluently, which may describe someone who is verbally energetic, but does not directly imply enthusiasm in action or eagerness. Thus, among the provided words, "alacrity" most accurately captures the spirit of being enthusiastic and energetic.