Ans. Let the hydrogen atoms be excited to n‌th ‌ energy level.
E‌=−13.6(‌

1

nf2

−‌

1

ni2

)‌‌[∵ni=1]
⇒12.3‌=(‌

1

12

−‌

1

n2

)
⇒‌‌12.3‌=13.6−‌

13.6

n2

⇒‌‌‌

13.6

n2

‌=13.6−12.3=1.3
⇒‌‌n2‌=‌

13.6

1.3

⇒n‌‌≈3
The formula for calculating the wavelength of Lyman series is given below:
‌

1

λ

=R(‌

1

12

−‌

1

n2

)
For second member of Lyman series, n=3
∴‌‌

1

λ

‌=R(1−‌

1

32

)
⇒‌

1

λ

=(1.09737×107)(‌

8

9

)
⇒λ=1025.1Å
The formula for calculating the wavelength of Balmer series is given below:
∴‌‌‌

1

λ

=R(‌

1

4

−‌

1

n2

)
For second member of Balmer series:
‌n‌=4
‌‌

1

λ

‌=R(‌

1

4

−‌

1

42

)
⇒‌‌

1

λ

=(1.09737×107)(‌

3

16

)
⇒λ‌=4861Å