Concept: Bond energy is the amount of energy required to break one mole of a particular bond in the gaseous state. It is influenced by factors such as bond length, bond order, and the size of the atoms involved. Generally, as the size of the atoms increases down a group, the bond length increases, and the bond energy decreases.

Why (A) is correct:

All the given bonds are single covalent bonds between identical atoms of Group 14 elements. As we move down Group 14 from Carbon (C) to Silicon (Si) to Germanium (Ge) to Tin (Sn), the atomic size increases. An increase in atomic size leads to an increase in bond length. Longer bonds are generally weaker and thus have lower bond energies because the shared electrons are further from the nuclei and experience less attraction.

Therefore, the C-C bond, being formed between the smallest atoms in the series, has the shortest bond length and consequently the highest bond energy among the given options.

Option Analysis:

• A) $\mathrm{C}-\mathrm{C}$: Carbon is the smallest atom among the given options. The C-C bond is relatively short and strong, resulting in high bond energy.
• B) $\mathrm{Si}-\mathrm{Si}$: Silicon is larger than carbon. The $\mathrm{Si}-\mathrm{Si}$ bond is longer and weaker than the $\mathrm{C}-\mathrm{C}$ bond, hence it has lower bond energy.
• C) $\mathrm{Ge}-\mathrm{Ge}$: Germanium is larger than silicon. The $\mathrm{Ge}-\mathrm{Ge}$ bond is longer and weaker than the $\mathrm{Si}-\mathrm{Si}$ bond, hence it has lower bond energy.
• D) $\mathrm{Sn}-\mathrm{Sn}$: Tin is larger than germanium. The $\mathrm{Sn}-\mathrm{Sn}$ bond is the longest and weakest among the given options, hence it has the lowest bond energy.

Correct Answer: (A)