Em tham khảo nha:
\(\begin{array}{l}
1)\\
m{\rm{dd}}spu = 100 + x(g)\\
mKCl = x + 100 \times 10\%  = 10 + x(g)\\
\dfrac{{10 + x}}{{100 + x}} = 15\%  \Rightarrow x = 5,88g\\
2)\\
m{\rm{dd}} = 5 + 20 + 400 = 425g\\
C\% NaN{O_3} = \dfrac{{20}}{{425}} \times 100\%  = 4,7\% \\
C\% KCl = \dfrac{5}{{425}} \times 100\%  = 1,18\% 
\end{array}\)