Answer:
First blank: 12CO2 (12 mole of Carbon dioxide)
Second blank: 13C (13 mole of Carbon)
Explanation: Algae requires carbon dioxide and water for synthesizing organic molecules in the presence of sunlight trapped by a pigment called chlorophyll A.
Algae makes use of CO2 from the extrinsic environment (water) to incorporate its biochemical activities, like energy production.
In the process of conversation, carbon molecules are lost to the external environment which in turn enriches surrounding rocks with Carbon.
