Question

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. What should be ionization energy of sodium atom in order of ${10}^{-19}$? (c = 3 $\times$ 10${}^8$ ms${}^{-1}$, h = 6.626 $\times$ 10${}^{-34}$ J s)

• A. $8.2$
• B. $8$
• C. $9$
• D. $9.2$

Answer 1

The correct option is A $8.2$

As we know,
$E=\frac{hc}{\lambda }$

$=\frac{6.626\times {10}^{-34}Js\times 3\times {10}^{8}m{s}^{-1}}{242\times {10}^{-9}J}$

$=8.2\times {10}^{-19}$