Answer
$3Mg(s)+N_2(g)\rightarrow Mg_3N_2(S)$
This is combination.
Work Step by Step
$Mg(s)+N_2(g)\rightarrow Mg_3N_2(S)$
This is a combination reaction because two elements are combining to form a compound.
Add a coefficient of 3 to $Mg$ to balance the equation.
$3Mg(s)+N_2(g)\rightarrow Mg_3N_2(S)$