What is the statute of limitations for general issues with tax returns?

What is the statute of limitations when there is a 25% understatement of gross income?

What is the statute of limitation on fraudulent or false returns?

What is the statute of limitations for refunds for individuals (aka an amended return)?

What is the statute of limitations on bad debts or worthless securities?

When is a taxpayer required to make an estimated quarterly tax payment?

On which form does a taxpayer submit a claim for a refund of erroneously paid income taxes?

What are the two appropriate methods to calculate the amount of estimated payments due?