Question

Which of the following molecules has the smallest dissociation energy?

• A. $L{i}_2$
• B. $N{a}_2$
• C. $K_2$
• D. $C{s}_2$

Answer 1

The correct option is D $C{s}_2$

$Cs$ lies in the first group towards the bottom, that is in the sixth period. As we go down a group, atomic radius increases. So, when two atoms of $Cs$ combine to form a $Cs$ molecule, their atomic radius being very large, the atoms are placed far from each other, and their orbitals do not overlap properly. So the bond formed between them, is very weak, as the orbitals do not overlap properly. Thus, the dissociation energy of $C{s}_2$ molecule is small. The bond can be easily broken down.

Option D is the correct answer.