The correct answer is Option (4) - A-iii, B-iv, C-i, D-ii
| COLUMN 1 |
COLUMN 2 |
| A. Methanogens |
iii. Production of methane |
| B. Fermentors |
iv. Large vessels for growing microbes |
| C. Organic waste in water |
i. BOD |
| D. Biogas |
ii. Methane-rich fuel gas |
A. Methanogens - iii. Production of methane
Methanogens are a type of archaea that produce methane as a metabolic byproduct. They are commonly found in environments like wetlands and the guts of animals, where they decompose organic material to produce methane.
B. Fermentors - iv. Vessels for growing microbes
Fermentors are specialized vessels used in the fermentation process to grow microorganisms. They provide a controlled environment for the microbial fermentation of various substrates, which can include bacteria, yeast, or fungi.
C. Organic waste in water - i. BOD
Organic waste in water contributes to the Biological Oxygen Demand (BOD), which is a measure of the amount of oxygen required by aerobic microorganisms to decompose organic matter in water. Higher BOD indicates higher levels of organic pollution.
D. Biogas - ii. Methane rich fuel gas
Biogas is a type of fuel gas that is primarily composed of methane. It is produced through the anaerobic digestion of organic matter, such as agricultural waste, manure, and other biodegradable materials. | 
