If 2.0 mol of Zn is mixed with 3.0 mol
of HCl, which reactant will be limiting?

The following Balanced Reaction will take place:

Zn + 2HCl → ZnCl₂ + H₂

In the question, we have 2 moles of Zinc and 3 moles of HCl for this reaction

Amount of HCl required to completely react with 2 moles of Zn:

Since we need 2 moles of HCl for every mole of Zn, we will need 2(2) = 4 moles of HCl for every 2 moles of Zn

Identifying the Limiting Reagent:

But we are only given 3 moles of HCl where we need 4 moles to completely react.

So, since HCl is in less amount, it is the Limiting Reagent