The word autotroph comes from the union of two words: auto from self, and trophos, from feed. Having this clear, we can say that autotrophs organisms are those kinds of organisms whose metabolisms allow them to produce their own food by the use of external sources of energy, such as the one from the sun, but also the one from heat, or the chemical processes.
There are different kinds of autotroph organisms, these are chemoautotrophs and photoautotrophs. We can find the last ones in the seas or in the forests, being them phytoplankton, and plants that carry out photosynthesis to produce glucose with the action of the sunlight and the intake of water, producing oxygen too after the process.
Having considered this, we can say that the correct answer is the first one, which states that autotrophs are "A. Organisms that take solar energy and convert it into chemical energy".