Issues with multiple checkboxes

I support the suggestion given Sikhi. It is important to maintain the relationship in database. As CME is a growing organisation, you would need a solution which would fit in the future needs of the client.
I would suggest to have 3 different ref tables.
1. To save the Exchange type (CMEEL, CEMCE, CBOT, CME, COMEX, NYMEX)
2. To save all possible Classes (Agricultural, Energy, etc).
3. The relationship between the two tables: For each row in exchange type.

Now if the user selects two exchange types from one region, then have the union of all possible classes and display them. And you will be able to store the class id for the application.
This structure will support if there are any addition of classes in future for any exchange type(s).

In addition to that, I would suggest to ask user for the UK / US exchange using a dropdown or radio option so that it would save your extra effort of hiding the irrelevant exchange types.

I support the suggestion given Sikhi. It is important to maintain the relationship in database. As CME is a growing organisation, you would need a solution which would fit in the future needs of the client.
I would suggest to have 3 different ref tables.
1. To save the Exchange type (CMEEL, CEMCE, CBOT, CME, COMEX, NYMEX)
2. To save all possible Classes (Agricultural, Energy, etc).
3. The relationship between the two tables: For each row in exchange type.

Now if the user selects two exchange types from one region, then have the union of all possible classes and display them. And you will be able to store the class id for the application.
This structure will support if there are any addition of classes in future for any exchange type(s).

In addition to that, I would suggest to ask user for the UK / US exchange using a dropdown or radio option so that it would save your extra effort of hiding the irrelevant exchange types.