Two members of the boron family owe their names to bright lines in their emission spectra. indium has a bright indigo blue line (451.1nm) and thallium has a bright green line (535.0 nm).
what are the energies of these two spectra lines?

E Indium =     4.407 x 10⁻¹⁹ J

E Thallium =  3.716 x 10⁻¹⁹ J

Explanation:

From Planck´s equation for a given wavelength, the energy is given by.

E = h ( c/ λ )

h: Planck´s constant, 6.626 x 10⁻³⁴ J·s

c: light speed, 3 x 10⁸ m/s

λ: wavelength in m

We will need first to convert the given wavelengths to m:

451.1  nm x ( 1 m/10⁹  nm ) = 4.511 x 10⁻⁷  m

535.0 nm x ( 1 m/10⁹ nm ) = 5.350 x 10⁻⁷ m

E Indium =    6.626 x 10⁻³⁴  J·s x 3x 10 ⁸ m/s/ 4.511 x 10⁻⁷  m = 4.407 x 10⁻¹⁹ J

E Thallium =  6.626 x 10⁻³⁴ J·s x 3x 10 ⁸ m/s/ 5.350 x 10⁻⁷ m = 3.716 x 10⁻¹⁹ J

the atomic number will stay the same no matter how many electrons it has, so it doesn’t decrease nor increase. it’ll only change with a different number of protons