Which adjective describes someone full of energy and cheerfulness?

The adjective that effectively describes someone full of energy and cheerfulness is "exuberant." This term conveys a sense of enthusiasm, vitality, and high-spiritedness, which aligns perfectly with the idea of being energetic and cheerful. When someone is described as exuberant, it implies they are not only lively but also radiating joy and enthusiasm in their demeanor and actions. This word captures the essence of a vibrant personality that can uplift and inspire others.

In contrast, the other options do not convey the same sense of energy or cheerfulness. "Pensive" refers to being engaged in deep or serious thought, often reflecting a somber mood. "Ponderous" describes something that is heavy, both in a physical sense or in terms of seriousness, which does not align with the idea of cheerfulness. "Dally" means to waste time or move slowly, suggesting a lack of energy or urgency rather than an abundance of cheer and enthusiasm. Overall, "exuberant" stands out as the most fitting choice for someone who embodies liveliness and joy.