Correct Option: A  [ photosynthesis ]
Remark:
Explanation: Photosynthesis is the process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂). This process takes place in the chloroplasts of plant cells, which contain the green pigment chlorophyll that captures solar energy.
Chemical Equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Thus, plants are known as autotrophs because they produce their own food using light energy — a process vital for sustaining all life on Earth.