Which of the following is an autotrophic mode of nutrition?

An autotrophic mode of nutrition refers to the ability of an organism to produce its food using simple inorganic substances such as carbon dioxide, water, and sunlight. Among the options listed, only chemosynthesis is an example of an autotrophic mode of nutrition. Chemosynthesis involves the synthesis of organic compounds by bacteria or other organisms using energy derived from the oxidation of simple inorganic compounds, such as hydrogen sulfide, instead of sunlight. This process is commonly found in deep-sea ecosystems, where there is no access to sunlight, and organisms rely on chemosynthesis to produce food. Therefore, the correct answer is chemosynthesis.