Question

Electromagnetic radiations of wavelength 242 nm is just sufficient to ionise Sodium atom. Then the ionisation energy of Sodium in kJ mole-1 is.

• A. 494.65
• B. 400
• C. 247
• D. 600

Answer 1

Answer: (A)

494.65

Answer 2

I.E. of one sodium atom $= \frac{hC}{\lambda}$

& I.E. of one mole Na atom

$= \frac{hC}{\lambda}_{N_{A}} = \frac{6.62 \times 10^{34} \times 3 \times 10^{8} \times 6.02 \times 10^{23}}{242 \times 10^{- 9}} = 494.65kJ.mol.$