Question

The colour of halogens progressively deepens from fluorine to iodine because:

• A. halogens of higher atomic number absorb light of longer wavelength since the difference in energy between the ground state and excited state decreases as the atomic number increases
• B. fluorescence and phosphorescence become more intense as the atomic numbers of halogen increases
• C. the standard electrode potential increases from $I_{2}to{F}_2$
• D. halogens of higher atomic number absorb light of shorter wavelength since the difference in energy between the ground state and excited state increases as the atomic number increases

Answer 1

The correct option is A halogens of higher atomic number absorb light of longer wavelength since the difference in energy between the ground state and excited state decreases as the atomic number increases

Halogens of higher atomic number absorb light of longer wavelength since the difference in energy between the ground state and excited state decreases as the atomic number increases. Energy difference = $-13.6\times \frac{Z^2}{N^2}\times \frac{1}{n_1^2-n_2^2}$ For higher states, the energy difference is less. And, since, $E=\frac{hc}{\lambda }$, lesser energy implies higher wavelength.