If 75% of the atoms are in the higher-energy parallel state, how many 21 cm photons are emitted per second by the cloud

If you chip a tooth, most likely you will go to the dentist to have the missing material filled in. currently the material used to fill in teeth is a polymer that is flexible when put in, yet is hardened to the strength of a tooth after irradiation with blue light at a wavelength of 461 nm. what is the energy in joules for a photon of light at this wavelength?

How many protons, electrons, and neutrons are in each of the following isotopes? a. zirconium-90 b. palladium-108 c. bromine-81 d. antimony-123

How many oxygen atoms are there in 3.15 moles of hcl manganese (iv) oxide, mno2