The ratio of electrostatic and gravitational forces acting between electron and proton separated by a distance $5 \times 10^{11} m$, will be (Charge on electron $=1.6 \times 10^{-19} C$, mass of electron $=9.1 \times 10^{-31} kg$, mass of proton $=1.6 \times 10^{-27} kg$ $\left.G=6.7 \times 10^{-11} Nm ^{2} / kg ^{2}\right)$