The pOH of a solution : 13.756
<h3>Further explanation</h3>
Mass HCl=10.4 g
mol HCl (MW=36.5 g/mol) :

Volume of HCl = 500 ml = 0.5 L

HCl ⇒ H⁺ + Cl⁻
[H⁺]=[HCl]=0.57 M
pH= - log[H⁺]
pH=-log[0.57]=0.244
pH+pOH=14
pOH=14-0.244
pOH=13.756
Refer to picture attached for solution