Question

Assertion In Lyman series of H-spectra, the maximum wavelength of lines is $121.65\, nm$.
Reason Wavelength is maximum if there is transition from the very next level.

• A. If both Assertion and Reason: are true and the Reason is the correct explanation of the Assertion
• B. If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion
• C. If Assertion is true but Reason is false
• D. If both Assertion and Reason are false

Answer 1

Answer: (A)

$\frac{1}{\lambda}=R_{ H } Z^{2}\left[\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right]$
For Lyman series, $n_{1}=1$
and $n_{2}=2$
$[\because$ for maximum $\lambda$, transition is from very next level.]
$\therefore \frac{1}{\lambda} =109678 \times(1)^{2}\left[\frac{1}{(1)^{2}}-\frac{1}{(2)^{2}}\right] cm ^{-1} $
or $=\frac{109678 \times 3}{4} cm ^{-1}$
$\lambda =\frac{4 \times 10^{7} \times 10^{-7}}{3 \times 109678} cm $
$=121.65\, nm $