Chapter 15 - Electric Charge, Forces, and Fields - Learning Path Questions and Exercises - Exercises - Page 556: 10

$13.5\times10^{-2} N$

Force = $k\frac{q_{1}q_{2}}{r^{2}}$ where $k=9\times10^{9}$ Carbon atom has 6 protons, Force = $k\frac{q_{1}q_{2}}{r^{2}}=9\times10^{9}\times \frac{(6\times1.6\times10^{-19})^{2}}{(0.25\times10^{-9})^{2}}=13.5\times10^{-2} N$