Option 1: Diesel is a commonly used fuel in vehicles and machinery. However, it releases harmful pollutants such as nitrogen oxide, sulfur dioxide, and particulate matter when burned, contributing to air pollution and negative impacts on the environment.

Option 2: Kerosene is a flammable hydrocarbon liquid commonly used as a fuel for heating and lighting. Like diesel, it also emits pollutants when burned, including carbon dioxide, nitrogen oxide, and sulfur dioxide. These emissions contribute to air pollution and global warming.

Option 3: Hydrogen is considered the cleanest fuel as it only produces water vapor when burned, resulting in minimal environmental pollution. It is a sustainable and renewable energy source that can be produced from various sources and used in fuel cells to generate electricity.

Option 4: Coal is a fossil fuel that releases significant amounts of carbon dioxide, sulfur dioxide, and other air pollutants when burned. It is a major contributor to greenhouse gas emissions, air pollution, and climate change.

Therefore, option 3, Hydrogen, causes the least environmental pollution compared to the other options.