If a taxpayer is married and files separately, what is the minimum gross income that requires them to file a return?

For a married taxpayer filing separately, the threshold for gross income that requires them to file a federal tax return is specifically set at a relatively low figure. In the case of this choice, the correct answer is indeed the minimum gross income requirement, which is $5. This threshold is significantly lower than that for other filing statuses.

It's important to note that even if a taxpayer's income is below this threshold, they may still choose to file a return for various reasons, such as claiming a refund of withholding or qualifying for certain credits. However, once a taxpayer's gross income meets or exceeds $5, they are obligated to file.

Other options provided, such as $2,000, $10,000, and $12,400, are incorrect in this context because they either represent filing thresholds for different filing statuses or are simply too high for a married individual filing separately. The specific requirement of $5 for this category reflects the way tax regulations have established filing requirements based on the potential for taxable income and the need for individuals to report their financial activity to the IRS.