Difference between ATP  and  ADP ?

Dear student,
Please find below the answer:

ATP is Adenosine triphosphate. It is the energy currency of life. One molecule of ATP contains three phosphate groups. ATP is the energy molecule that gives energy to the cells.

ADP  is Adenosine di-phosphate.  One molecule of ADP contains two phosphate groups. The purpose of ADP is to have to potential to store energy.

When ATP releases energy the third phosphate comes off and it becomes ADP. This conversion from ATP to ADP is an extremely crucial reaction for the supply of energy for life.

Hope this clears your doubt.
Regards.