Explanation:
The figure that accompanies the question shows the wavelenghts of the photons emitted according to Balmer series transition , from energy levels (n) 3, 4, 5, and 6 to the energy level (n) 2, in hydrogen atoms.
These are the values shown in the figure
Transition wavelength of the photon emitted
nm
from n = 3 to n = 2 656 <------------- this is the value requested
from n = 4 to n = 2 486
from n = 5 to n= 2 434
from n = 6 to n = 2 410
The wavelength of a photon emitted from the n = 3 shell in hydrogen is the first data of the table, i.e 656 nm.
Using the conversion factor from nm to m that result is:
656 nm * 1 m / (10^9 nm) = 656 * 10 ^ - 9 m.
