Answer:
The base in ATP (Adenosine Triphosphate) is **adenine**.
Step-by-step explanation:
Adenine is one of the four nitrogenous bases found in nucleotides, and in the case of ATP, it is combined with ribose (a sugar) and three phosphate groups. Adenine plays a crucial role in the structure and function of ATP, which is often referred to as the "energy currency" of the cell due to its role in energy transfer and storage in living organisms.