Question

The equation for the chemical reaction shown is not balanced. What number should replace the question mark to balance this equation?

Answer 1

I do believe that 2AlCl3 is saying two of the entire molecule.
2Al+?Cl2=2AlCl3
I like to multiply it out, even though it has no real significance.
2Al+?Cl2=Al2Cl6
?Cl2=Cl6
Divide by the two there
?Cl=3Cl
So B.

Answer 2

Thank you !