In a sludge tank, the gas mainly produced, is

Solution (By Examveda Team)

In a sludge tank, the decomposition of organic matter takes place under anaerobic conditions. During this process, microorganisms break down organic solids and produce gases as by-products.

The main gases generated are methane (CH₄) and carbon dioxide (CO₂). Since methane is not included in the given options, carbon dioxide is the correct answer.

Oxygen and nitrogen are not produced during anaerobic digestion, and hydrogen is formed only in very small quantities compared to carbon dioxide.