Validating records in a block

I have a requirement to validate records in a block such that if records are identical, then Form_Trigger_Failure exception could be raised. How can I achieve this in EBS 12.1.3? Is there a way using personalization or customization?

Example:

If user enter A in first column and B in second column, then repeat these values again in same columns then error message should be shown and Form_Trigger_Failure exception could be raised.