What are main energy levels

The main energy levels are the shells where the electron resides in a location that's relative to the atom's nucleus.

Explanation:

In electronic configuration in chemistry, the main energy levels are the shells where the electron resides in a location that's relative to the atom's nucleus. Such an energy level is usually denoted by the principal quantum number n. So n can be 1,2,3,4...e.t.c

organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.

all eukaryotic cell have mitochondria : )