Mixture a was made by mixing different components together, but it appears to have one phase. which term best categorizes mixture a?

Mixture A is a solution. Solutions are homogeneous and appear in one phase after mixing different components together. These components will be indistinguishable in the mixture. Solutions are composed of the solute and the solvent. Solute is the substance to be dissolved while solvent is the substance performing the dissolving. 

All the elements are arranged by melting points on the periodic table. in row they go from metals to gasses. in the row from sodium to argon, sodium is more reactive than the one on its right, magnesium.