Let's analyze each option:
(1) Nucleus:
Both animal and plant cells have a nucleus. It is not absent in plant cells, so this is not the correct answer.
(2) Centrosome:
The centrosome is present in animal cells and plays a role in cell division. It is not present in plant cells. Hence, this is the correct answer.
(3) Chloroplast:
Chloroplasts are found in plant cells and are responsible for photosynthesis. They are not present in animal cells, so this is not the correct answer.
(4) Endoplasmic reticulum:
The endoplasmic reticulum is present in both animal and plant cells. Therefore, this is not the correct answer.
Conclusion:
The correct answer is Option 2: Centrosome as it is present in animal cells but absent in plant cells.