The boiling points of ${\mathrm{CH}}_3{\mathrm{COCH}}_3,{\mathrm{CH}}_3{\mathrm{COC}}_2{\mathrm{H}}_5$ and ${\mathrm{CH}}_3{\mathrm{COC}}_3{\mathrm{H}}_7$ are ${56}^{\circ }\mathrm{C},{80}^{\circ }\mathrm{C}\text{,}$and ${102}^{\circ }\mathrm{C},$ respectively. This increase is best attributed to an increase in which of the following?

(P) Dipole-dipole interactions
(Q) Dispersion forces
(R) Hydrogen bonding

Intermolecular attractions increase as a molecule's number of electrons increases. The London dispersion forces also rise with size. More energy is required to separate the molecules from one another due to the molecules' greater attraction to one another. Consequently, the boiling point rises.

The boiling points of ${\mathrm{CH}}_3{\mathrm{COCH}}_3 , {\mathrm{CH}}_3{\mathrm{COC}}_2{\mathrm{H}}_5$, and ${\mathrm{CH}}_3{\mathrm{COC}}_3{\mathrm{H}}_7$ are 56° C, 80° C, and 102° C, respectively. This increase is best attributed to dispertion force.

Hence, option B is correct.