Answer :
There has to be a small 2 at the bottom right of Cl (sorry I cannot write 2 under Cl as a small number, but I hope you understand what I mean):
Al + Cl2 —> AlCl3
If you are requesting for it to be balanced, it would be:
2 Al + 3 Cl2 —> 2 AlCl3
Al + Cl2 —> AlCl3
If you are requesting for it to be balanced, it would be:
2 Al + 3 Cl2 —> 2 AlCl3