The electron transport chain primarily takes place in the mitochondria.
The mitochondria are known as the powerhouses of the cell, where energy production occurs through cellular respiration. During this process, electrons are transferred through a series of proteins embedded in the inner mitochondrial membrane. This transfer of electrons helps to create an electrochemical gradient that ultimately leads to the production of ATP, the energy currency of the cell.
While chloroplasts are involved in the light reactions of photosynthesis and do have an electron transport chain of their own, the question specifically refers to where electron transport occurs in the context of cellular respiration, which is indeed in the mitochondria. The cytoplasm is where glycolysis takes place, and ribosomes are primarily involved in protein synthesis, not electron transport.