# Estimate the difference in energy between first and second Bohr's orbit for a H atom.At what minimum atomic no a transition from $n=2$ to $n=1$ energy level would result in the emission of $X$-rays with $\lambda=3\times 10^8m$ ?which hydrogen atom like species does this atomic no corresponds to ?
$\begin{array}{1 1}(a)\;10.2eV,2&(b)\;9.8eV,3\\(c)\;81.3eV,4&(d)\;5.3eV,1\end{array}$