Correct answer is 17

$\begin{array}{rl}& \mathrm{\Delta }\mathbf{E}=\mathbf{1}\mathbf{0}\mathbf{.}\mathbf{2}\mathrm{eV}\\ & \text{ Recoil speed }(\mathrm{v})=\frac{\mathrm{\Delta }\mathrm{E}}{\mathrm{mc}}\\ & =\frac{10.2\mathrm{eV}}{1.6\times {10}^{-27}\times 3\times {10}^8}\\ & =\frac{10.2\times 1.6\times {10}^{-19}}{1.6\times {10}^{-27}\times 3\times {10}^8}\\ & \mathrm{v}=3.4\mathrm{m}/\mathrm{s}=\frac{17}{5}\mathrm{m}/\mathrm{s}\end{array}$

Therefore, $x=17$

Correct answer is 144

$\begin{array}{rl}& \frac{1}{\lambda }={\mathrm{RZ}}^2(\frac{1}{3^2}-\frac{1}{4^2})={\mathrm{RZ}}^2(\frac{1}{9}-\frac{1}{16})\\ & =\frac{7{\mathrm{RZ}}^2}{9\times 16}\\ & \Rightarrow \lambda =\frac{144}{7\mathrm{R}}\text{ for }\mathrm{Z}=1\therefore \alpha =144\end{array}$