<p>An excited&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mi>H</mi><msup><mi>e</mi><mo>+</mo></msup></math>&nbsp;ion emits two photons in succession with wavelength 108.5 and 30.4 nm respectively. The quantum no. n&#39; corresponding to its initial excited state is: E =&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mfrac><mn>120</mn><mrow><mi>&#955;</mi><mo>&#160;</mo><mo>(</mo><mi>n</mi><mi>m</mi><mo>)</mo></mrow></mfrac><mi>e</mi><mi>V</mi></math></p>