The element with atomic number 12 is Magnesium.
(a) 1s²2s²2p⁶3s² is the electronic configuration of Mg.
(b) Mg is in IIA group .
(c) Mg is a metal.
(d) Magnesium chloride's formula is MgCl₂.
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the element is MAGNESIUM 
a. electronic configuration = 2,8,2

b. it belongs to group II A 
c. it is a metal
d. formula of magnesium chloride is MgCl₂  
i hope it helps...........
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