Final answer:
The 3-year statute of limitations for filing a refund claim is extended to 7 years in specific tax-related situations involving the claim of a loss from worthless securities or a bad debt deduction.
Step-by-step explanation:
When addressing the question of when the 3-year statute of limitations for filing a claim for refund is extended to 7 years, it is important to understand that this extension typically applies in specific tax-related situations. Specifically, the statute of limitations can be extended if the taxpayer has paid a portion of their income for a claim of a loss from worthless securities or a bad debt deduction, which necessitates a longer period for the taxpayer to realize the loss and seek a refund.