Answer
$2Al(s)+3Cl_2(g)\rightarrow 2AlCl_3(s)$
This is combination.
Work Step by Step
$Al(s)+Cl_2(g)\rightarrow AlCl_3(s)$
This is a combination reaction because two elements are combining to form a new compound.
$Cl$ is even on the left and odd on the right. Use a coefficient of 2 on $AlCl_3$ to make the count even to enable balancing.
$Al(s)+Cl_2(g)\rightarrow 2AlCl_3(s)$
Use a coefficient of 2 on $Al$ to balance $Al$.
Use a coefficient of 3 on $Cl$ to balance $Cl$.
$2Al(s)+3Cl_2(g)\rightarrow 2AlCl_3(s)$
