What happens when two things in a collision push on each other

In which of the following belong to a category called the main group of elements? nonmetals. transition elements. halogens. alkali metals. it can be more than one answer!

What is the molality of a solution that has 4 mol of kci in 0.800 kg of water

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?