Choose the answer which presents the chemical formulas for two substances in order of decreasing melting point (highest melting point first) and gives a valid reason for this order.
a) C6Cl6 > C6H6 due to ionic bonding in C6Cl6 not present in C6H6.
b) PbO2 > PbCl4 due to lower molar mass of PbO2.
c) SiF4 > Si because of the layered molecular structure of Si.
d) SeO2 > SiO2 due to the higher molar mass of SeO2.
e) HF > HCl because HF has hydrogen bonding and HCl does not.