3. To study microbial activity in a stream sediment, an engineer took some stream water and sediment samples back to the lab and set up an experiment as follows. 20-g (dry weight) sediment was added to a sealed 25 -liter barrel filled with the stream water. The stream water initially contained 10mg/ liter of oxygen. Assume 35% of the sediment dry weight is organic compound in a simplified formula of CH2O. a. Write the relevant reaction for O2 consumption and the amount of electrons transferred [10 points ] b. Would the barrel eventually become anaerobic? [Hint: this is a calculation question and requires calculation-based argument] [20 points ] c. The engineer found the stream water also contained 10 ppm SO42, how much SO42 would remain in the barrel after all reactions completed? [Hint: use Eq. 2.55 in the textbook for the reaction between CH2O and SO42 and pay attention to the amount of electrons transferred; this is a calculation question and requires calculation-based argument] [20 points]