In this question we are given the mols of HCl as 0.171 mols and the volume of the solution id 0.300L
we are required to find the molarrity of the solution.
molarity can by found by the equation
M = n/V
were M is Molarity and n is number of molds and V is the volume of the solution.
so the answer is
M =0.171/0.300
= 0.570 M