Question

An electric field E can pull an electron out of a Helium atom in the same time that the electron takes
to go around the nucleus once. Then E is?

Answer 1

It will be possible when force produced by the electric field will be equal to the force produced by the electrostatic force of attraction between nucleus and electron

$eE=\frac{kZe^2}{r^2}\\E=\frac{k.4e}{r^2}$