Which of the following bond has lowest energy? 1.C-C. 2.N-N 3.H-H 4.O-O 5.F-F I don't understand the concept behind this question. If we take electronegative as a factor than option 5 is correct. And,if we take size a factor than H-H is correct. But,both are wrong .I also not getting which factor should I imply here.So,please please explain this question and also the factors on which it depends.
This is a table for bond energies. You can compare the bonds you mentioned and notice that H-H bond is the strongest. The weakest bond is O-O bond. The key factor is the bond length.
Lets remember that the chemical bond is a result of attraction between nuclei and electrons that occupies orbitals. This obeys the coulomb's law for electrostatic interaction, the bigger the charge the stronger the interaction and the farther the charges from each other the weaker the interaction.
So, reasonable factors that are underlying the bond length may be the nearness of the electrons to the nuclei (s or p or d or f, etc.) and the effective charge of the nuclei (the word effective here is important because, if the shell containing the electrons is high the nuclei would be shielded by other electron that resides in lower shells, thus resulting in less charge the electron in the high shell can feel).
On the other hand the number of protons increases the effective charge that's why F-F is stronger than O-O although the Florine atom is bigger.
This is a useful link: http://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.html
Hope this helps, and don't hesitate to ask for any further clarification if needed.