Question

For a single ionized helium atom ,the longest wavelength in ground state will absorb

• A. 912 ${}^{0}A$
• B. 304 ${}^{0}A$
• C. 606 ${}^{0}A$
• D. 1216 ${}^{0}A$

Answer 1

The correct option is B 304 ${}^{0}A$

For Helium atom, $Z=2$

Longest wavelength, $\frac{1}{\lambda }=R{Z}^2(\frac{1}{n_1^2}-\frac{1}{n_2^2})$ where $n_1=1$ and $n_2=2$

$\therefore$ $\frac{1}{\lambda }=1.097\times {10}^{-3}\times \left(2^2\right)(\frac{1}{1}-\frac{1}{2^2})$

$⟹$ $\lambda =304$ $A^o$