Answer:
See the answer below
Step-by-step explanation:
When an object on a sample slide can be perfectly focused at lower objective but cannot be focused at higher objectives, the problem can be attributed to two factors depending on the size of the objective:
1. At 40X objective, the most likely problem would be that the object on the sample slide is not in the center of the field. Adjusting the slide until the object on it is at the center of the field would likely solve this problem.
2. At 100X objective, the problem could also be that the object on the slide is not at the center of the field, could be that there is no immersion oil on the slide or a combination of the two factors. Dropping an immersion oil on the slide and adjusting the slide to bring the object on it to the center would solve this problem.