An electron is moving around the nucleus of a hydrogen atom in a circular orbit of radius r. What is the coulomb force $\overrightarrow{\mathrm{F}}$ between the two? \(\left ( \text{where},K=\frac{1}{4\pi \epsilon _{0}} \right )\)

1. $\mathrm{K}\frac{{\mathrm{e}}^2}{{\mathrm{r}}^2}\hat{\mathrm{r}}$

2. $-\mathrm{K}\frac{{\mathrm{e}}^2}{{\mathrm{r}}^3}\hat{\mathrm{r}}$

3. $\mathrm{K}\frac{{\mathrm{e}}^2}{{\mathrm{r}}^3}\overrightarrow{\mathrm{r}}$

4. $-\mathrm{K}\frac{{\mathrm{e}}^2}{{\mathrm{r}}^3}\overrightarrow{\mathrm{r}}$