How do you calculate experimental mole ratio?

By Dividing the moles of the reactants by the moles of the experiments. 
Let's the chemical equation: 
We know that 1.20 g of Al is reacting with 2.40g of I2
and check the periodic table, and u'll see that the mass of 1 atom of Al is 26.98 and the mass of 1 atom of I2 is 253.8 g
First, you convert every single mass you got into moles.



Now, it's time to find the molar ratio
The mole of the reactant is 0.04448 mol, and the experiments are 0.009456 mol.
You divide reactant over experiments, and you get:
= 

So, the experimental molar ration of the  experiment I2 is 

Hope this Helps :)