Final answer:
The energy needed to create hydrogen and oxygen gas comes from an external electricity source, such as a battery, using the process of electrolysis. This hydrogen can be used for fuel in fuel-cell vehicles, offering an environmentally friendly alternative to fossil fuels.
Step-by-step explanation:
The energy required to create hydrogen and oxygen gas primarily comes from an external power source, such as a battery, which supplies electrical energy. This process is known as electrolysis, where an electric current is passed through water to decompose the water molecule (H₂O) into its constituent gases: hydrogen (H₂) and oxygen (O₂). The hydrogen produced can serve as a clean fuel for fuel-cell vehicles (FCV), which are more efficient and environmentally friendly compared to traditional internal combustion engines, since they do not emit pollutants and reduce greenhouse gas emissions.