\( \text { Recoil speed(v) }=\frac{\Delta \mathrm{E}}{\mathrm{mc}} \)
\( =\frac{10.2 \mathrm{eV}}{1.6 \times 10^{-27} \times 3 \times 10^8} \)
\( =\frac{10.2 \times 1.6 \times 10^{-19}}{1.6 \times 10^{-27} \times 3 \times 10^8} \)
\( \mathrm{v}=3.4 \mathrm{~m} / \mathrm{s}=\frac{17}{5} \mathrm{~m} / \mathrm{s}\)
Therefore, \(x=17\)