Which of the following contain a delocalized pi h2o, o3, hcn, co3^2-

You should remember that a pi bond is related to an alkene, compounds that have a double bond. Among the choices, the only compound that has a double bond is the CO3^2-. Since it is an ion, the pi electrons are delocalized, meaning, their location cannot be indicated as they rotate around the molecules. This is a result of following the octet rule.

This would be canberra.

Iam not going to tell you