When is a married couple filing jointly required to file if their gross income is $21,800?

A married couple filing jointly is required to file a tax return if their gross income meets or exceeds the threshold set by the IRS for the specific tax year. For the tax year in question, the threshold for a married couple filing jointly is $20,150. Since their gross income is $21,800, which exceeds this threshold, they are required to file a return.

This requirement is established to ensure that all individuals and couples with income above a certain level contribute fairly to federal obligations and also allows for the potential to benefit from tax credits and deductions that might apply to them. In the case at hand, the couple needs to file because their income surpasses the necessary filing threshold, making option A the correct choice.

The other options do not pertain directly to the income threshold that determines filing requirements. Factors such as having children, one spouse being self-employed, or owing state taxes are not determinants for the necessity to file, but rather context-specific scenarios that can influence the overall tax situation or filing outcomes.