An example of a double reaction is
a. 2ag + s → ag₂s
b. zn + 2hci → znci₂ + h₂
c. feci₂ + na₂co₃ →

C. is the only double reaction here given that a double replacement reaction involves two compounds that exchange previous components, and C is the only solution with two compounds present

The answer is water molecules are split.cellular respiration and photosynthesis are complement  reactions to each other. these are reverse reactions. in cellular respiration glucose and oxygen yield water and carbon dioxide. so, when respiration begins,  glucose molecules are split. in the opposite reaction - in photosynthesis, carbon dioxide and water yield glucose and oxygen. thus,  when respiration begins, water molecules are split.