Methanogens do not produce:

The correct answer is Option (4) → Nitrogen and Oxygen

Methanogens are anaerobic bacteria, such as Methanobacterium, that grow on cellulose-rich material in sewage sludge, biogas plants and the rumen of cattle.

Option (1) Carbon dioxide and methane — Produced by methanogens.

Option (2) Methane and Hydrogen — Produced by methanogens.

Option (3) Hydrogen and Carbon dioxide — Produced by methanogens.

Option (4) Nitrogen and Oxygen — Not produced by methanogens. They are anaerobic and give no oxygen; nitrogen is not among their products either.

NCERT Extract:
Microbes in Production of Biogas – “… In the examples cited in relation to fermentation of dough, cheese making and production of beverages, the main gas produced was CO₂.. However, certain bacteria, which grow anaerobically on cellulosic material, produce large amount of methane along with CO₂ and H₂. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium.”