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Choose the answer which presents the chemical formulas for two substances in ord

ID: 753215 • Letter: C

Question

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) PH3 > NH3 due to dipole-dipole forces in PH3 not present in NH3. b) PbCl4 > PbO2 due to lower charge on Cl - than O2-. c) NaF > MgF2 due to the lower molar mass of NaF. d) Si > SiF4 due to covalent-network bonding in Si, versus dispersion forces in SiF4. e) SiO2 > SeO2 due ionic bonding in SiO2 but not in SeO2.

Explanation / Answer

c) NaF > MgF2 due to the lower molar mass of NaF.