The statement that best describes the effect of low ionization energies and low electronegativities on metallic bonding is the first one - the valence electrons are easily delocalized.
Due to these low energies and negativities, valence electrons can be moved around quite easily and their positions may be altered quite drastically.
No. Magnesium, and Bromine are a chemical compound when put together.
Neither Bromine, nor Magnesium react with any sort of water.