Question

${\lambda }_1$ and ${\lambda }_2$ are wavelengths of the first line of Balmer series of deuterium and hydrogen respectively, then:

• A. ${\lambda }_1>{\lambda }_2$
• B. ${\lambda }_1<{\lambda }_2$
• C. ${\lambda }_1={\lambda }_2$
• D. ${\lambda }_1\ge {\lambda }_2$

Answer 1

Answer: (B)

${\lambda }_1<{\lambda }_2$

According to Bohr model,
$\frac{1}{\lambda }=\overline{v}=R_H\cdot Z^2[\frac{1}{n_1^2}-\frac{1}{n_2^2}]$

As $n_1$ and $n_2$ are same for both and

$R_H$ for $D=109708c{m}^{-1}$ and $R_H$ for $H=109678c{m}^{-1}$.

So, ${\lambda }_1<{\lambda }_2$