air
In air it is called snow or ice fog
On a solid it is called frost or hoar
In water it is called frazil ice
in the center. Its called a Nucleus. It controlls the atom
white blood cells
It's called the Mantle
Flowers are actually quite complex. They have several parts which allow for polination and seed development. The best way to find out the specific part of the flower that you are looking for is to find a diagram and look for the labeled part. There technically isn't enough information in your question to name the particular part.
If you were talking about which storm has an ''eye'' I have an answer for you. In hurricanes, the center dot is what is called its ''eye''. It is the most calmest part of a hurricane, believe it or not.
The center
I believe, although I may be incorrect, that the center, or core for that matter, is still a part of the pith, the white stuff on the peel.
the center part of the tree is called the core.
the yellow part of an egg is called the yolk, and the white part is called the egg white also called the albumen.
The center of the planet is called the "core."
the edge
The white part of an egg is called the (Egg white). It's also called albumen.
The white of the eye is called the Sclera.
It is called the hub.
the red and white part
puke
The center of the nut or the edible part is generally called the "nut meat" or the kernel.