Arrange the following:
H-H, D-D and F-F in order of increasing bond dissociation enthalpy.

Explanation

The bond dissociation enthalpy of the bond is the lowest (242.6 kJ`cdot "mol"^(-1)`) and this is due to high concentration of electron density around each F atom in the form of three unshared pair which cause significant repulsive interactions. Again, because of marginally smaller size of D as compared to H, the bond dissociation enthalpy of the D-D bond (443.35 kJ`cdot" mol"^(-1)` ) is slightly higher than that of the H-H bond (435.88 kJ`cdot " mol"^(-1)` ). Hence, the bond dissociation enthalpy increases in the order: F - F `lt` H - H D - D .