Đáp án:
16,25%
Giải thích các bước giải:
\(\begin{array}{l}
mNaOH\,trong\,{\rm{dd}}\,10\% = m{\rm{dd}} \times C\% = 150 \times 10\% = 15g\\
mNaOH\,trong\,{\rm{dd}}20\% = m{\rm{dd}} \times C\% = 250 \times 20\% = 50g\\
mNaOH = 15 + 50 = 65g\\
m{\rm{dd}} = 150 + 250 = 400g\\
C\% NaOH = \dfrac{{mct}}{{m{\rm{dd}}}} \times 100\% = \dfrac{{65}}{{400}} \times 100\% = 16,25\%
\end{array}\)
