Una partícula alfa, el núcleo de un átomo de helio, tiene una masa de 6.64*10^(-27) kg y una carga de +2e, ¿Qué magnitud y dirección del campo eléctrico balancearan su peso?

Remember that the nucleus of an athom is neutral, which means protons, neutrons and electrons have the same and opposite charge so that the net electircal field is zero. In that case, we say the nucleus is estable.

Now, to mantain the equilibrium of the given element, we need an electrical field equal in magintude +2e with opposite direction, that will balance it.