Qué ciencia estudia la estructura y relaciones en sustancias que no contiene carbono

Write the symbol for every chemical element that has atomic number greater than 3 and atomic mass less than 12.0 u.

Can someone me with questions 15 to 17 plz.

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.