Answer:
Generally, oil immersions are used when one has to witness the cells from the inside and is mostly seen at 100X objective. The oil immersions are used to cope with the RI or the refractive index, as when light goes from a substance of one RI to the substance of another RI the light gets scattered.
One is not able to see the cells when the slide is placed upside down, however, when the slide was turned over then everything becomes clear. As basically when we look through the microscope then initially the top thread comes into focus succeeded by the middle and eventually the bottom one.
However, when one put the slide upside down then at that time the slide function as the first thread and the cells function as the second thread. As the slide is formed of dense and thick substance it is tough to focus the second thread or the cells via it. This is the reason that one is not able to witness anything when the slide is kept in this position.
<span>The oceanic crust is part of the crust that is made fully out of basaltic rock and is several times thinner than the continental crust which is made out of granitic rock. Oceanic crust underlies Earth's oceans and is produced at divergent plate boundaries which are commonly referred to as mid-ocean ridges. As it grows from infilling magma and spreads away from the ridges, it will becomes cooler, thicker, and more dense, and will eventually sink into the mantle.</span>
