**C-H Bond Dissociation Energy**

The C-H bond dissociation energy (BDE) refers to the energy required to break the bond between a carbon (C) atom and a hydrogen (H) atom in a molecule. It is a measure of the strength of the C-H bond and can vary depending on the molecular structure and surrounding functional groups.

**Comparing BDE of Different Compounds**

To determine which of the given compounds possesses the C-H bond with the lowest bond dissociation energy, we need to consider the factors that influence bond strength. Generally, the BDE tends to decrease with increasing substitution on the carbon atom bonded to hydrogen.

Let's compare the given compounds:

**a) Toluene**

Toluene is an aromatic compound with a benzene ring substituted by a methyl group. The methyl group provides some degree of electron donation to the benzene ring, which increases the electron density around the carbon atom bonded to hydrogen. This increased electron density weakens the C-H bond, resulting in a lower bond dissociation energy compared to benzene.

**b) Benzene**

Benzene is an aromatic compound with a ring of six carbon atoms, each bonded to a hydrogen atom. Benzene has a higher BDE compared to toluene due to the absence of any electron-donating groups that could weaken the C-H bond.

**c) n-Pentane**

n-Pentane is an alkane compound with a straight chain of five carbon atoms and twelve hydrogen atoms. Alkanes have C-H bonds with relatively high BDEs because they lack any functional groups that could influence electron density. Therefore, n-pentane is expected to have a higher C-H BDE compared to toluene and benzene.

**d) 2,2-Dimethyl Propane**

2,2-Dimethyl propane is an alkane with four carbon atoms and ten hydrogen atoms. Similar to n-pentane, it lacks any functional groups that could affect electron density. Therefore, the C-H BDE of 2,2-dimethyl propane is expected to be higher than that of toluene and benzene.

**Conclusion**

In conclusion, of the given compounds, benzene is expected to have the highest C-H bond dissociation energy, followed by toluene, n-pentane, and finally 2,2-dimethyl propane. The presence of electron-donating groups in toluene and the absence of any such groups in benzene contribute to the differences in their C-H BDEs. Alkanes like n-pentane and 2,2-dimethyl propane have higher BDEs due to the absence of any functional groups that could influence electron density.

no...dear i to thot dat ans wud be n- pentane but its toluene....& so i want the reason for it