Hướng dẫn:

${{n}_{NaOH}}={{V}_{NaOH}}.{{C}_{{{M}_{NaOH}}}}=0,1.3=0,3\left( mol \right)$

$C{{H}_{3}}COOH+NaOH\to C{{H}_{3}}COONa+{{H}_{2}}O$

   0,3           $\leftarrow $  0,3                                             (mol)

Theo phương trình ta có:

${{n}_{NaOH}}={{n}_{C{{H}_{3}}COOH}}=0,3\left( mol \right)$

$C%=\frac{{{m}_{NaOH}}}{{{m}_{\text{d}{{\text{d}}_{NaOH}}}}}.100=\frac{12}{200}.100=6\left( % \right)$

$\Rightarrow $Chọn đáp án C