Question

The difference between the wave number of 1st line of Balmer series and last line of paschen series for Li2+ ion is :

• A. $\frac{R}{36}$
• B. $\frac{5R}{36}$
• C. 4R
• D. $\frac{R}{4}$

Answer 1

Answer: (D)

$\frac{R}{4}$

Answer 2

For 1st line of Balmer series

$= R_{H}(3)^{2}\left\lbrack \frac{1}{(2)^{2}} - \frac{1}{(3)^{2}} \right\rbrack = 9R\left( \frac{5}{36} \right) = R$

For last line of Pachen series

$= R_{H}(3)^{2}\left\lbrack \frac{1}{(3)^{2}} \right\rbrack - \frac{1}{(\infty)^{2}} = r$

so, $- = \frac{5}{4}R - R = \frac{R}{4}$.