The third answer is the one you want. You have to have an adjustable density. All other things being equal, if the tanks you use for holding just water when filled with water will let the sub sink, because the sub is made of a dense metal like iron or steel.
If on the other hand you fill these tanks with air, the net density will be below one and the sub will rise.
It means it is an ion. It has lost two protons making it a positive ion.
Ionic bonds are formed from the attraction of oppositely charged ions in a chemical compound
I believe it is NaCl(aq) + H2O
