Which of the following processes releases energy to be used by a cell?

a. a phosphate group is added to atp to form adp.
b. a phosphate group is added to adp to fprm atp
c. a phosphate group is removed from adp to form atp
d. a phosphate group is removed from atp to form adp

D. a phosphate group is removed from atp to form adp

ATP usually releases energy by breaking down the weak phosphate cell present.  The energy released due to the breaking down of the phosphate cell is then utilized. The ATP is converted to ADP. Whenever a cell feels the necessity for energy it releases a phosphate to gather the energy. It is an automatic and ongoing process. The weak bond between the second and the third phosphate is always targeted for turning ATP to ADP. This is the reason ATP is considered the main energy currency for the cell. 

The light is great source of energy