Answer:
x4 objective
Step-by-step explanation:
The student should use the x4 objective lense in order to be able to observe the palisade cell of a leaf.
The palisade cells are located below the cuticle and the epidermis of the leaf and the x4 objective will provide the largest field of view for adequate study by the student. The x4 objective is also easier to focus compared to the lower objectives.