An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r . Find the coulomb force $\;\overrightarrow{F}\;$ between the two

Question

$(a)\;\large\frac{ke^2}{r^2}\;\hat{r}\qquad(b)\;\large\frac{ke^2}{r^3}\;\overrightarrow{r}\qquad(c)\;-\large\frac{ke^2}{r^3}\;\hat{r}\qquad(d)\;-\large\frac{ke^2}{r^3}\;\overrightarrow{r}$