Right option is (a) Highest calorific value
Explanation: The calorific value of methane gas is 55mJ/Kg which can be used as a fuel and natural gas has the lowest calorific value, eutrophication leads to algal blooms which deteriorates the health of aquatic life, BOD determines the amount of oxygen which is consumed by the organic matter present in water. Eutrophication is harmful to aquatic life.