\(r= \frac{1}{4 \pi \epsilon _0} \frac{ze^2}{K.E.}\)
\(K.E. = 1.6 \times 10^6 \times 1.6 \times 10^{-19}\)
\(= 2.56 \times 10^{-13} J\)
\(r = \frac{9 \times 10^9\times 79\times (1.6\times 10^{-19})^2}{2.56 \times 10^{-13}}\)
\(= \frac{9 \times 10^9 \times 79 \times 1.6 \times 1.6 \times 10^{-38}}{2.56\times 10^{-13}}\)
\(= 9 \times 79 \times 10^{-16} = 711 \times 10^{-16} m\)
\(R \approx 71.1 fm\)
