During decomposition, which of the following nutrients is released?

During decomposition, organic matter is broken down by microbial activity, leading to the release of various nutrients into the soil. Among the options provided, nitrogen plays a crucial role during this process.

Nitrogen is a fundamental nutrient for plants and is often present in organic matter in the form of proteins and nucleic acids. As microorganisms break down this organic matter, they convert complex organic compounds into simpler forms, releasing nitrogen primarily as ammonium and then as nitrate through further processes such as nitrification. This nitrogen becomes available for plant uptake, promoting growth and development.

The other nutrients listed, such as calcium, boron, and chlorine, are also essential for plant nutrition but are not primarily released during decomposition in the same way nitrogen is. Calcium tends to be more stable in the soil, boron is usually found in trace amounts, and chlorine is not a major focus in the context of decomposition processes. Thus, nitrogen's release during decomposition significantly supports soil fertility and plant health, making it the correct answer.