Is Martin required to file as Single after his divorce in December even if he supported Rita all year?

Martin is required to file as Single after his divorce in December, regardless of whether he supported Rita all year. When an individual gets divorced, their filing status for the tax year is primarily determined by their marital status on the last day of the year. In this case, since Martin's divorce was finalized in December, he is no longer considered married for the entirety of the year, and therefore, he cannot file as Married Filing Jointly or Married Filing Separately.

Supporting Rita throughout the year may affect other aspects of his taxes, such as eligibility for certain credits or deductions, but it does not change his marital status for filing purposes. The option indicating that he can file as Head of Household is not applicable since to qualify for that status, one must be unmarried and maintain a household for a qualifying person, which typically would require that the taxpayer not be divorced by the end of the tax year.