\(n_{Zn\left(OH\right)_2}=\dfrac{a}{99}\) mol
\(n_{H^+}=n_{HCl}=0,2.1,5=0,3\) mol
\(Zn\left(OH\right)_2+2H^+\rightarrow Zn^{2+}+2H_2O\)
0,3 \(\leftarrow\) 0,6
\(Zn\left(OH\right)_2+2OH^-\rightarrow ZnO_2^{2-}+2H_2O\)
0,3 \(\rightarrow\) 0,6
\(\Rightarrow n_{NaOH}=n_{OH^-}=0,6\) mol
\(\Rightarrow m_{NaOH}=40.0,6=24\) gam