Alarge number of hydrogen atoms are excited from the ground state to the state with n = 4. at how many different wavelengths may photons be emitted by this group of atoms?

6

Explanation:

Following are the possible transition

1 ) 4 to 3

2) 4 to 2

3) 4 to 1

4 ) 3 to 2

5 ) 3 to 1

6 ) 2 to 1 .

There are altogether 6 wavelengths of photons possible .

This result can be achieved with the help of permutation and combination.

No of ways in which 2 things can be selected out of 4 things , combination being all different.

₂C⁴ = (4 X 3) / 2 = 6.