Question

which of the lewis structures given below is the best structure for ocl₂?

Explanation:

Step1: Determine valence electrons

O has 6 valence - electrons and each Cl has 7 valence - electrons. So for $OCl_2$, the total number of valence electrons is $6 + 2\times7=20$.

Step2: Analyze octet rule and formal charges

In the structure $\ddot{Cl}-\ddot{O}-\ddot{Cl}$, each atom has an octet of electrons around it. The formal charge on O is $6 - 4 - 2 = 0$, and the formal charge on each Cl is $7 - 6 - 1 = 0$.
In structures with double - bonds between O and Cl, the formal charges will not be zero for all atoms or some atoms will have an expanded octet which is not favorable for these second - row elements.

Answer:

The structure $\ddot{Cl}-\ddot{O}-\ddot{Cl}$ (the second structure in the image) is the best Lewis structure for $OCl_2$.