Question

select the part whose main job is to send instructions to different parts of the cell. chloroplast cytoplasm nucleus mitochondria

Explanation:

The nucleus contains genetic material (DNA) which holds the instructions for the cell's activities. It sends these instructions (via mRNA etc.) to different parts of the cell to regulate functions like protein synthesis, metabolism etc. Chloroplasts are for photosynthesis, cytoplasm is the fluid - filled space where organelles are suspended, and mitochondria are for energy production (ATP synthesis).

Answer:

nucleus