According to Bohr's theory, Energy of electron in nth orbital of H-atom with Atomic number (Z) = \(-13.6\frac{2^2}{n^2}\)eV
\(\therefore\) The energy of ground state electron in H-atom = -13.6 eV
Now, it absorbs 12.1 eV energy.
So, its energy increase to -13.6 + 12.1 = - 0.85 eV
\(\therefore\) E = -13.6\(\frac{z^2}{n^2}\)eV
-0.85 = -13.6 x \(\frac{(1)^2}{n^2}\) (\(\because\) for hydrogen Z = 1)
\(\therefore\) n2 = \(\frac{13.6}{0.85}\) = 16
\(\therefore\) n = 4
Hence, the electron in H-atom jumps to 4th orbit on absorbing 12.1 eV energy.