Answer and Explanation:
To draw the Lewis structure we have to make sure taht each element in the molecules complies the Octet rule, in which each element has 8 electrons during a bond in its valence shell, or 2 electrons in the case of hydrogen.
• O3:
We can see that in the O3 molecule, each oxygen atom has 8 electrons, but in this case we can write 2 different structures, that's why the Lewis structure of O3 is called resonant.
• HOCl:
In the HOCl molecule the oxygen atom and the chlorine atom has an Octet with 8 electrons and the hydrogen atom has an Octet with 2 electrons.
• HCN:
In the HCN molecule, the atoms of carbon and nitrogen have an Octet with 8 electrons, and the atom of hydrogen has an Octet with 2 electrons.