\(\begin{array}{l} a)\\ C\% NaOH = \dfrac{{50}}{{100}} \times 100\% = 50\% \\ C\% KCl = \dfrac{{25}}{{100}} \times 100\% = 25\% \\ b)\\ C\% NaOH = \dfrac{{0,5 \times 40}}{{200}} \times 100\% = 10\% \\ C\% KCl = \dfrac{{0,2 \times 74,5}}{{200}} \times 100\% = 7,45\% \end{array}\)