(solved)Question 2.10 of NCERT Class XI Chemistry Chapter 2

Sodium atom (Z = 11) has 1 valence electron

$\displaystyle \therefore $1 photon required to ionize the sodium atom

Given: 1 photon $\displaystyle \lambda = 242 \text{ nm}$ just ionizes one atom

Energy due to 1 photon, by Planck's equation

$\displaystyle E = \frac{hc}{\lambda} \text{ (J)}$

but 1 mol photon needed to ionize 1 mol sodium

$\displaystyle \text{IE/mol} = \frac{hc}{\lambda} \times 6 \times 10^{23} \text{ (J)}$

$\displaystyle = \frac{6.6 \times 10^{-34} \times 3 \times 10^8}{242 \times 10^{-9} \text{ m}} \times 6 \times 10^{23} \text{ (J)}$

$\displaystyle = 491 \text{ kJ/mol }\underline{Ans}$