Answer:
The production of hydrogen releases CO₂.
Step-by-step explanation:
Hydrogen is not a primary fuel, it means that it is not available to be used directly, it must be produced. The production generally uses fossil fuels, and in that case, CO₂ is produced, which is a greenhouse gas (GHG).
So, to obtain that fuel, CO₂ is released, which has a negative effect on the environment because it intensifies the greenhouse effect and global warming.