Final answer:
The ideal objective for observing parasite ova under a microscope is the oil immersion objective lens.
Step-by-step explanation:
When observing parasite ova under a microscope, the ideal objective to use is the oil immersion objective lens. This lens has the highest magnification power and resolution, making it suitable for viewing small objects like parasite ova. The oil immersion lens achieves a total magnification of 1000X with a resolution of 0.2 µm, allowing for detailed examination of the ova.