The melting and boiling points of molecular compounds are generally quite low compared to those of ionic compounds. This is because the energy required to disrupt the intermolecular forces between molecules is far less than the energy required to break the ionic bonds in a crystalline ionic compound
19) 6,50% because (as you said) the law of definite proportions states that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass
