Is the dot structure method failproof? in other words, are there any exceptions or is this the best way to determine oxidation states for "non-obvious" compounds?

This _is_ the best method to determine the oxidation states for non obvious compounds as far as I know.

However, dot structures are not perfect; for instance, they are really useful for simple mechanisms, but fail to explain to explain the behaviors and regioselectivity of other reactions (such as Wittig reactions for instance).

Ithink carbon dioxide, i am not completely sure.tell me if i am wrong.

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.