Which molecule is formed when ATP loses a phosphate during energy release?

• A. Adenosine Triphosphate (ATP)
• B. Adenosine Diphosphate (ADP)
• C. Adenosine Monophosphate (AMP)
• D. Pyrophosphate (PPi)

Answer: (B)

When ATP loses its terminal phosphate through hydrolysis, the molecule that remains is ADP, Adenosine Diphosphate. ATP contains three phosphate groups; breaking the bond of the last phosphate releases a free inorganic phosphate (Pi) and energy that the cell can use for work. This conversion—ATP plus water producing ADP plus Pi—is the main way cells couple energy release to processes like muscle contraction and active transport. If another phosphate is removed later, ADP can become AMP, but the immediate product of the energy-releasing step is ADP with Pi released. Pyrophosphate is a separate species and not the typical product of this single phosphate loss.