I only need number #12. I don’t understand it at all :( can someone pls help?

Bohr's model could only explain the spectra of which type of atoms? single atoms with one electron single atoms with more than one electron bonded atoms with one electron bonded atoms with more than one electron

Often on a topographic map, every fifth contour line is darkened. what is this line called? a. key b.slope c.benchmark d. index contour

Americium-241 undergoes fission to produce three neutrons per fission event. if a neutron-absorbing material is mixed in with this sample so that the rate of neutron production drops down to 1.8 neutrons per fission event, which will be effective at achieving a critical mass? check all that apply. remove a deflective shield surrounding the sample. remove absorbent material mixed in with the sample. compress the sample of americium-241.