Question

Which of the following bonds is the strongest?
A.$F - F$
B.$I - I$
C.$Cl - Cl$
D.$Br - Br$

Answer 1

Hint: To answer this question you must recall the factors that affect the strength of the bond between two atoms. When the bond is formed between atoms of the same element having same electronegativity, the bond formed is by the sharing of electrons equally by the two atoms. The strength of this bond formed depends on the electronic configuration of the outermost shell or the valence shell of the atoms.

Complete answer:
As we move from top to bottom in a group, the size of the valence shell increases and so does the size of the orbitals. Thus, the bonds formed are not very stable. Based on this information, we can say that in a group, the strength of the bond between the atoms of the same element decreases.
So according to this, $F - F$ bond is expected to be the strongest among all the halogens. However, due to the exceptionally small size of the fluorine atom, the bond is exceptionally weak. Two fluorine atoms forming the bond face internuclear repulsion due to close proximity thus weakening the bond. The strongest bond is $Cl - Cl$.

Thus, the correct answer is C.
Note:
As we move across a period from left to right in the periodic table, the number of electrons in the valence shell keeps on increasing and the atomic size keeps on decreasing as a result. Since the number of electrons in the shell increases and the size of the shell decreases, it becomes more crowded. This leads to higher inter electronic repulsions and this repulsion causes the electrons to move away and hence the bond formed is strong.