Since you provided no answer choices, I will assume the correct answer choice is ANCESTOR. A cladogram begins with a common ancestor of all the organisms represented above.
This would be 7. Below 7 is acidic and above is basic. 7 is neutral
It is an atom with a charge of 0 because a positive atom would be +1 charge and a negative atom would be -1 charge. So neutral would just be 0
They help convert nitrogen to nitrate which is usable by living beings. (Living beings can't use regular nitrogen)
