Bohr's model of the hydrogen atom posits that an electron's angular momentum \( L \) in orbit is quantized, defined by \( L = n\hbar \). Here, \( n \) represents the principal quantum number, and \( \hbar \) denotes the reduced Planck’s constant. The radius of the \( n \)-th orbit in a hydrogen atom follows \( r_n \propto n^2 \). Consequently, \( n \) can be expressed in relation to \( r \) as \( n \propto \sqrt{r} \). Substituting this into the angular momentum equation yields \( L \propto n \propto \sqrt{r} \). Therefore, the angular momentum of an electron in a hydrogen atom is directly proportional to \( \sqrt{r} \).
