autotrophs are organisms that can synthesise organic compounds (e.g.: carbohydrates) from inorganic C compounds (e.g.: CO2)
Phototrophs are those use photons also known as light energy, chemotrophs are those who utilize chemical energy as their source of energy. chemotrophs can either use inorganic or organic molecules as source of energy. from the options given there are 2 answers with CO2, the correct combination is CO2 with inorganic compounds
Therefore chemoautotrophs use inorganic compounds as an energy source and CO2 as a carbon source