Let $E_{n}=\frac{-1}{8 \epsilon_{0}^{2}} \frac{m e^{4}}{n^{2} h^{2}} \quad$ be the energy of the nth level of H-atom. If all the H-atoms are in the ground state and radiation of frequency $(E_2-E_1)/h$ falls on it
(a) it will not be absorbed at all
(b) some of the atoms will move to the first excited state
(c) all atoms will be excited to the $n=2$ state
(d) no atoms will make a transition to the $\mathrm{n}=3$ state