When $\text{ CsI, }{\mathrm{SiO}}_2,{\mathrm{CH}}_3\mathrm{OH}$and ${\mathrm{C}}_3{\mathrm{H}}_8$ are listed in order of increasing melting point, which is the correct order?

The order of increasing melting point for the given molecules is,

$\underset{(\mathrm{Molecular} \mathrm{lattice}}{{\mathrm{C}}_3{\mathrm{H}}_8}<\underset{(\mathrm{Molecular} \mathrm{lattice} ) }{{\mathrm{CH}}_3}-\mathrm{OH}<\underset{\mathrm{Ionic} \mathrm{lattice}}{\mathrm{CsI}}<\underset{(\mathrm{Covalent} \mathrm{lattice})}{{\mathrm{SiO}}_2}$Thus, correct option is D.