The correct option is B I>II>III>IV
With increase in the molecular weight, the boiling point also increases.
The order of the atomic weights of halogens is I>Br>Cl>F.
Hence, the correct order of the boiling point is I>II>III>IV or CH3CH2−II>CH3CH2−BrII>CH3CH2−ClIII>CH3CH2−FIV.