This is a limiting reactant problem.
One way to solve it is to figure out how much product you could get from each reactant separately.
To do that you need the molar ratio between each reactant and the product.
The balanced chemical equation is
#"LiOH" + "HCl" → "LiCl" + "H"_2"O"#
From #"LiOH"#:
The molar ratio is #"1 mol LiCl"/"1 mol LiOH"#
∴ #"Moles of LiCl" = 3 color(red)(cancel(color(black)("mol LiOH"))) × ("1 mol LiCl")/(1 color(red)(cancel(color(black)("mol LiOH")))) = "3 mol LiCl"#
From #"HCl"#:
The molar ratio is #"1 mol LiCl"/"1 mol HCl"#
∴ #"Moles of LiCl" = 1.75 color(red)(cancel(color(black)("mol HCl"))) × ("1 mol LiCl")/(1 color(red)(cancel(color(black)("mol HCl")))) = "1.75 mol LiCl"#
#"HCl"# gives fewer moles of #"LiCl"#, so #"HCl"# is the limiting reactant.
The theoretical yield of #"LiCl"# is 1.75 mol.
