In the chemical reaction, mg + 2hcl mgcl2 + h2 how many moles of hcl are needed to completely react with 3.5 moles of mg?

The balanced equation for the above reaction is as follows;
Mg + 2HCl ---> MgCl₂ + H₂
stoichiometry of Mg to HCl is 1:2
number of Mg moles reacted - 3.5 mol
1 mol of Mg reacts with 2 mol of HCl 
therefore 3.5 mol of Mg requires - 2 x 3.5 = 7.0 mol of HCl 
number of HCl moles required to completely react with 3.5 mol of Mg is 7.0 mol of HCl