Final answer:
The correct option is 1)Chemical energy.
In the absence of sunlight, autotrophs like chemoautotrophs use chemical energy to produce organic compounds through chemosynthesis. These organisms are able to thrive in environments devoid of sunlight by oxidizing inorganic substances.
Step-by-step explanation:
When there is no sunlight available, autotrophs such as chemoautotrophs rely on chemical energy as their source of fuel. These autotrophs use chemicals in their environment to perform chemosynthesis, a process similar to photosynthesis but without the need for sunlight. Chemoautotrophs include certain types of bacteria and archaea that can be found in environments like hydrothermal vents or hot springs, where they utilize inorganic chemical compounds to produce organic molecules necessary for survival.
Unlike photoautotrophs that make use of solar energy through photosynthesis to assemble organic compounds, chemoautotrophs obtain energy by oxidizing inorganic substances such as hydrogen sulfide, ammonium, and ferrous iron. This adaptation allows them to thrive in environments where sunlight is not available. As a result, in the absence of the sun, autotrophs may turn to chemical energy to maintain their metabolic processes and sustain their role as primary producers in certain ecosystems.