The correct answer is option 2: Chloroplasts.

Photosynthesis, the process by which plants convert sunlight into energy, takes place inside the chloroplasts of plant cells. Chloroplasts are specialized organelles found in plant cells that contain a pigment called chlorophyll. This pigment is responsible for capturing light energy from the sun.

Option 1: Ribosomes, are small organelles responsible for protein synthesis and are not involved in photosynthesis.

Option 3: Nucleus, is the control center of the cell that contains the genetic material. While the nucleus plays a role in regulating cellular activities, it is not directly involved in photosynthesis.

Option 4: Mitochondria, are organelles responsible for cellular respiration and generate energy in the form of ATP. They are not involved in photosynthesis.

Therefore, the correct answer is option 2: Chloroplasts.