What is the electron configuration of an electrically neutral atom of magnesium?

The electron configuration of an atom can be determined by identifying first the right order of the electron shells. The atomic number of Magnesium is 12 so we expect the electrons also sum up to 12. The condensed electron configuration is Ne 3s2. The complete configuration is 1s2  2s2 2p6 3s2. 

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It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).