<p>The Bohr&#39;s energy equation for H-atom reveals that the energy level of a shell is given by E = -13.58/<math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>n</mi><mn>2</mn></msup></math>&nbsp;eV. The smallest amount that an H-atom will absorb, if in ground state is:</p>