In order to find the number of moles of tin (IV) chloride produced, we need to set up the properly balanced equation first:
Sn + 2 Cl2 -> SnCl4
Now that the reaction is balanced, we can see that the molar ratio between Cl2 and SnCl4 is 2:1 (according to the coefficients), which means that we need 2 moles of Cl2 in order to produce 1 mol of SnCl4, therefore if we have 2.85 moles of Cl2:
2 Cl2 = 1 SnCl4
2.85 Cl2 = x moles of SnCl4
2x = 2.85
x = 2.85/2
x = 1.42 moles of SnCl4 is produced from 2.85 moles of Cl2