## College Physics (7th Edition)

The gravitational force is $=G\frac{m_{1}m_{2}}{r^{2}}$, The electric force is $=k\frac{q_{1}q_{2}}{r^{2}}$. The mass of proton is in the range of $10^{-27}$kg, so the gravitational force will be very much smaller than the electric force. (d) is the answer.