Due to electron deficiency in a metal cation, they cannot form a covalent bond beacuse it means to share electrons. By contrast metal cation seek for electrons. In an ionic bond, one atom give electrons, while another atom recevie electron. Because of that, this is the better option to metal cations.
A. Whatever is in the water, it moves. Even if a block is placed in there, it would move by sinking to the bottom. If a plastic bag was placed in there, it wouldn't sink but move a little.