Between which two orbits of the Bohr hydrogen atom must an electron fall to produce light of wavelength 434.2 ?

Answer 1

434.2 WHAT?
1/wavelength = R(1/ni^2 - 1/nf^2)

wavelength goes in in units of meters.
Look up the Rydberg constant
nf^2 = unknown
ni^2 = 2^2 = 4
Solve for the unknown.