The correct answer is option 2: Methane. Methane gas is released from rice fields in the most prominent quantities.

Methane is a greenhouse gas that is produced as a byproduct of the anaerobic (without oxygen) decomposition of organic matter in flooded rice fields. Rice fields are flooded to provide the ideal conditions for rice cultivation, but this also creates a low oxygen environment in the soil. In this environment, microorganisms break down organic matter, such as dead plant material and organic fertilizers, and release methane gas.

Carbon dioxide, option 1, is also released from rice fields, but in lesser quantities compared to methane. Carbon dioxide is a byproduct of the overall process of plant photosynthesis and respiration.

Carbon monoxide, option 3, and sulphur dioxide, option 4, are not typically released from rice fields. Carbon monoxide is a gas produced by incomplete combustion, while sulphur dioxide is commonly associated with burning sulfur-containing fuels or industrial processes.

In summary, while all the options listed may be associated with various processes, methane gas is released from rice fields in the most prominent quantities.