1. For an electron revolving in a hydrogen atom, the electrostatic force provides the centripetal force:

$\frac{m v^2}{r} = \frac{1}{4\pi\varepsilon_0}\frac{e^2}{r^2}$

2. Rearranging:

$m v^2 = \frac{1}{4\pi\varepsilon_0}\frac{e^2}{r}$

So,

$v^2 \propto \frac{1}{r}$

Hence,

$v \propto \frac{1}{\sqrt{r}}$

3. The angular momentum of the electron is

$L = mvr$

Since $m$ is constant,

$L \propto vr$

Substitute $v \propto \frac{1}{\sqrt{r}}$:

$L \propto r \cdot \frac{1}{\sqrt{r}} = \sqrt{r}$

4. Therefore, the angular momentum is proportional to

$\sqrt{r}$

So the correct option is C.