I believe it would be a fossil of a reptile but I'm not a 100% sure about it.
A water molecule (H2O) will have a slightly positive side, and a slightly negative side. The oxygen side of water is the one that is negative, while hydrogen side tends to be more positive. When a molecule has a half negative and half positive side like water does, it is called a polar molecule. :D
You are likely referring to active immunity that can come from naturally acquiring the disease or vaccines. Both have T cells that fight pathogens and more antibodies are created to recognize viruses and the like and neutralize them. B cells can make more antibodies. There is a lot more detail to this question but hope it helps. Have a good day.
Yes it is true you are very smart :) let me know if this is helpful