Suppose an electron in an atom experiences an attractive force towards the nucleus given by $F = k/r$,where $k$ is a constant and $r$ is the distance of the electron from the nucleus. Applying the Bohr model to this system,the radius of the $n^{th}$ orbit $r_n$ and the kinetic energy of the electron in that orbit $K_n$ are found. Which of the following relationships is correct?

• A
  $K_n \propto 1/n, r_n \propto n^2$
• B
  $K_n \propto 1/n^2, r_n \propto n^2$
• C
  $K_n$ is independent of $n$; $r_n \propto n$
• D
  $K_n \propto 1/n, r_n \propto n$