For which tax is a contractor responsible on a quarterly basis?

A contractor is responsible for paying federal unemployment tax on a quarterly basis as part of their payroll tax obligations. This tax is specifically meant to fund unemployment benefits for workers who lose their jobs through no fault of their own. The federal unemployment tax is generally assessed on the first $7,000 of each employee's wages per year, and it is crucial for maintaining the benefits system for unemployed individuals.

In contrast, Social Security tax and Medicare tax are typically withheld from employees' wages and are matched by the employer, but they are reported and paid on a different schedule, generally alongside payroll taxes rather than on a quarterly basis. State income tax varies by state and is also not universally required to be reported or paid quarterly, as it can depend on individual state laws and the contractor's specific tax situation. Thus, federal unemployment tax is specifically mandated to be filed quarterly, making it the correct answer in this context.