Final answer:
Fossil fuels have the highest negative H_rcn due to their carbon emissions and negative environmental impacts.
Step-by-step explanation:
The energy source with the highest negative Hrcn is Fossil fuels (option a).
Fossil fuels, such as natural gas, coal, and oil, release carbon dioxide (CO2) and other greenhouse gases when burned, resulting in negative environmental impacts.
These emissions contribute to climate change and air pollution.