Prokaryotes are the only group of organisms capable of using inorganic compounds as a source of energy.

Explanation:
Prokaryotes are a diverse group of unicellular organisms that lack a nucleus and membrane-bound organelles. They include bacteria and archaea. Prokaryotes have the ability to use inorganic compounds as a source of energy through various metabolic processes.

Key points:
Here are some key points to further explain why prokaryotes are the only group capable of using inorganic compounds as a source of energy:

1. Chemolithotrophy: Prokaryotes have the unique ability to perform chemolithotrophy, a process in which they use inorganic compounds as a source of energy. Chemolithotrophic prokaryotes obtain energy by oxidizing inorganic compounds like ammonia, hydrogen sulfide, iron, and various other minerals.

2. Energy production: Inorganic compounds serve as electron donors in the metabolic pathways of chemolithotrophic prokaryotes. These compounds undergo oxidation-reduction reactions, releasing energy that is used for ATP production through processes such as oxidative phosphorylation or substrate-level phosphorylation.

3. Inorganic compound utilization: Prokaryotes possess enzymes and metabolic pathways that enable them to utilize inorganic compounds as energy sources. For example, nitrifying bacteria can oxidize ammonia to nitrite or nitrate, while sulfur-oxidizing bacteria can oxidize hydrogen sulfide or elemental sulfur.

4. Ecological significance: Prokaryotes that utilize inorganic compounds play crucial roles in various ecosystems. For instance, nitrifying bacteria are essential in the nitrogen cycle, converting ammonia to nitrite and nitrate. Sulfur-oxidizing bacteria contribute to the sulfur cycle by oxidizing sulfide to sulfate.

5. No other groups: Eukaryotes, which include plants, animals, fungi, and protists, rely on organic compounds as energy sources and are unable to directly use inorganic compounds for energy production. Viruses, although they can infect prokaryotes and eukaryotes, are not considered living organisms and do not possess the metabolic machinery to utilize inorganic compounds.

In conclusion, prokaryotes are the only group of organisms capable of using inorganic compounds as a source of energy due to their unique metabolic abilities and enzymatic pathways.