Which of the answer choices correctly describes covalent bonds?

a) an attraction between oppositely charged ions
b) a force that holds atoms or ions together in a fixed structure or unit
c) a sharing of four pairs (eight valence electrons) between two atoms
d) a sharing of an electrons pair between two atoms

50.)the diagram below represents the wave fronts produced by a point source moving to the right in a uniformmedium. observers are located at points a and b.compared to the wave frequency and wavelength observed at point a, the wave observed at point b has a(1) higher frequency and a shorter wavelength(2) higher frequency and a longer wavelength(3) lower frequency and a shorter wavelength(4) lower frequency and a longer wavelength