How many unpaid electrons are in 1s2 2s2 2p6 3s2 3p6

In numbering carbon atoms in the parent chain of a hydrocarbon, why would you number from right to left, rather than left to right

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?

Which fact represents evidence for the big bang theory?