We understand tht metals pretty much form bonds by losing their valence (outermost electrons). But this question specifically asks for metals that lose beyond their outermost electrons; next to outermost principal energy levels.
Pb, Mg, and Ca only lose their outermost electrons to form the following ions;
Pb2+, Mg2+, and Ca2+.
This is because their ions have achieved a stable octet configuration - the dreamland of atoms where they are satisfied and don't need to go into reactions again.
Iron on the other hand has the following electronic configurations;
Fe: [Ar]4s2 3d6
Fe2+: [Ar]4s0 3d6
Fe3+: [Ar]4s0 3d5
This means ion can lose both the ooutermost electrons (4s) and next to outermost principal energy levels (3d). So correct option is Iron.
In the older procedure, the solution is cooled so quickly that the recrystallization can be less effective. By allowing the solution to cool slowly, the maximum amount of crystal is formed, and also the impurities are trapped, so the process is more controlled than by the older one.
<span>According to its definition, the answer is: The characteristics that best describe the tail of a phospholipid molecule are </span><span>a. neutral charge, nonpolar, and hydrophobic</span>
