Đáp án đúng: D
0,13M.
${{\text{n}}_{\text{NaOH}}}\text{=}\frac{\text{400}\text{.0,16}}{\text{40}}\text{=1,6}\,\text{mol;}\,{{\text{n}}_{\text{FeC}{{\text{l}}_{\text{3}}}}}\text{=}\frac{\text{500}\text{.0,1625}}{\text{162,5}}\text{=0,5}\,\text{mol}$
$\begin{array}{l}\text{F}{{\text{e}}^{\text{3+}}}\text{+3O}{{\text{H}}^{\text{-}}}\xrightarrow{{}}\text{Fe(OH}{{\text{)}}_{\text{3}}}\downarrow \\\text{0,5}\,\to \,\,\text{1,5}\,\,\,\,\xrightarrow{{}}\,\,\,\,\,\,\,\text{0,5}\end{array}$
$\Rightarrow {{\text{V}}_{\text{dd}\,\text{X}}}\text{=}\frac{\text{400+500-0,5}\text{.107}}{\text{1,1}}\text{=769,55}\,\text{ml}\Rightarrow {{\text{C}}_{\text{M}\,\text{NaOH}}}\text{=}\frac{\text{1,6-1,5}}{\text{0,7696}}\text{=0,13}\,\text{M}$
