Which sequence lists the following ionic compounds in order of decreasing melting point (highest to lowest)?
Al2O3, SrO, MgF2, KCl
a) SrO > Al2O3 > MgF2 > KCl
b) Al2O3 > MgF2 > SrO > KCl
c) Al2O3 > SrO > MgF2 > KCl
d) Al2O3 > SrO > KCl > MgF2