Final answer:
Form 941 is used by employers to report federal withholding, social security tax, and Medicare tax on a quarterly basis.
Step-by-step explanation:
The form used by an employer to report federal withholding, social security tax, and Medicare tax is Form 941. This form is filed quarterly. Form 941 is used to report the employer's portion of Social Security and Medicare taxes, as well as federal income tax withholding on wages paid to employees.