Mg + Cl2 redox reaction explain?

The metal loses electrons, and in forming #Mg^(2+)# it loses 2 electrons and is oxidized:

#Mg(s) rarr Mg^(2+) + 2e^-# #(i)#

And on the other hand chlorine is reduced to chloride ion by accepting electrons:

#Cl_2(g) +2e^(-) rarr 2Cl^(-)# #(ii)#

E #(i) + (ii)=# #Mg(s) + Cl_2(g) rarr MgCl_2(s)#

Both charge and mass are balanced, as required.