Sources of Arsenic Contamination:

Intense exploitation of groundwater:
- Arsenic contamination in groundwater is a significant issue in many parts of the world, particularly in regions where groundwater is intensively exploited.
- When groundwater is excessively pumped from aquifers, it can cause the water table to lower, leading to the intrusion of contaminants from surrounding areas into the aquifer.
- Arsenic can be naturally present in rocks and minerals, and when the water table drops, it can mobilize and contaminate the groundwater.

Weathering of rocks and minerals followed by leaching and runoff:
- Arsenic is naturally present in rocks and minerals such as arsenopyrite and arsenic-bearing sulfides.
- Over time, weathering processes break down these rocks and minerals, resulting in the release of arsenic into the environment.
- Arsenic can then leach into the soil and water, where it can contaminate groundwater and surface water through runoff.

Iron coprecipitation:
- Iron coprecipitation is a process where arsenic binds with iron minerals in the environment.
- When iron minerals are present in soils or sediments, arsenic can adsorb onto their surfaces and become immobilized.
- However, under certain conditions, such as changes in pH or redox potential, the iron minerals can dissolve, releasing the bound arsenic back into the environment.

Burning of coal:
- Arsenic is naturally present in coal, and when coal is burned for energy production or other industrial processes, it releases arsenic into the atmosphere.
- The released arsenic can then be deposited onto land, water bodies, and vegetation, leading to contamination.

Correct answer: Only three (c)

Explanation:
- The sources of arsenic contamination mentioned in options a, b, and d are all correct.
- Intense exploitation of groundwater can lead to the intrusion of arsenic from rocks and minerals into the aquifer.
- Weathering of rocks and minerals followed by leaching and runoff is a natural process that can release arsenic into the environment.
- Iron coprecipitation is a mechanism by which arsenic can bind with iron minerals and later be released under certain conditions.
- However, burning of coal is not a direct source of arsenic contamination in terms of groundwater or natural environment. It primarily contributes to atmospheric deposition of arsenic onto land and water bodies.
- Therefore, the correct answer is option c, which states that only three of the statements are correct.