<span>It is known as the axon</span>
Explanation:
No. Isotopes are atoms of the same element with different atomic masses (due to the different number of neutrons)
For example, carbon exists as carbon-12 and carbon-14, which both have 6 protons but have 6 and 8 neutrons respectively.
Water, lower, and I'm not too sure for the third one... sorry.
