Convert 3.4 moles of Hcl to grams

3.4 mol HCl * (36.46 g / 1 mol) = 123.964 g HCl = 1.2 x 10^2 g HCl

Convert moles of HCl to grams of HCl using the molar mass (36.46 g/mol).

Revise your answer to have the right number of significant figures (2 significant figures in this case, as determined by the the number of figures in the value with the least figures).

1 mole HCl=1+35.5=36.5g

3.4moles HCl=3.4*36.5=124.1g