Which of the following is a natural agent of purification in water quality management?

Wetlands and natural vegetation are considered a natural agent of purification in water quality management due to their ability to filter and cleanse water through natural biological processes. Wetlands serve as a buffer that captures pollutants, sediments, and excess nutrients from surface runoff before they enter larger bodies of water. The plants in these ecosystems contribute to the removal of contaminants by absorbing nutrients and breaking down organic materials, which can enhance water quality.

Natural vegetation also plays a role by stabilizing soil, reducing erosion, and promoting biodiversity within the ecosystem, which can further aid in the water purification process. The biological activities of microbes and other organisms in these natural systems can also help decompose harmful substances, leading to improved water clarity and quality.

In contrast, other options like chemical coagulants, mechanical filtration systems, and chlorine compounds rely on artificial processes and methods to treat water rather than harnessing the inherent capabilities of natural systems. While these methods are effective in their own right, they don't represent the same natural purification processes demonstrated by wetlands and vegetation.