Biochemical oxygen demand (BOD) is the amount of oxygen required (in ppm):
By bacteria to break-down organic waste in a certain volume of water sample.
The Explanation for the correct option:
BOD also called biological oxygen demand, is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature.
The Explanation for the incorrect option:
It is not the photochemical breakdown of waste.
Biochemical oxygen demand (BOD) is not the amount of oxygen required by anaerobic bacteria to break-down inorganic waste present in a water body.
So, option (C) is correct.