(i) Two atoms of the same element combine to form a molecule. The bond between them is known as bond. (ii) Two chlorine atoms combine to form a molecule. The bond between them is known as . (iii) In forming oxygen molecule, electrons are shared by each atom of oxygen. (iv) In forming N2 molecule, electrons are shared by each atom of nitrogen. (v) The number of single covalent bonds in C2H2 molecule are . (vi) Melting points and boiling points of ionic compounds are generally than those of covalent compounds.