Question

Assertion Balmer series lies in the visible region of electromagnetic spectrum.
Reason $\frac {1}{\lambda}=R \bigg [\frac {1}{2^2}- \frac {1}{n^2} \bigg ],$ where $ n=3,4,5 $

• A. Both assertion and reason are true and reason is the correct explanation of assertion
• B. Both assertion and reason are true but reason is not the correct explanation of assertion
• C. Assertion is true but reason is false
• D. Both assertion and reason are false

Answer 1

Answer: (A)

The wavelength in Balmer series is given by
$ \frac {1}{\lambda}=R \bigg [\frac {1}{2^2}- \frac {1}{n^2} \bigg ], \, n=3,4,5,.... $
$ \frac {1}{\lambda_{max}}=R\bigg [\frac {1}{2^2}- \frac {1}{3^2} \bigg ] $
$ \frac {1}{\lambda_{max}}=\frac {36}{5R}= \frac {36}{5 \times 1.097 \times 10^7}=6563 \mathring {A} $
and $ \frac {1}{\lambda_{min}}=R \bigg [\frac {1}{2^2}- \frac {1}{\infin^2}\bigg ]$
$ \lambda_{min}= \frac {4}{R}= \frac {4}{1.097 \times 10^7}=3646 \mathring {A} $
The wavelength $6563 \, \mathring {A} \, and \, 3646 \, \mathring {A}$ lie in visible region.
Therefore, Balmer series lies in visible region.