The correct answer is B) Tenure of Office.
Congress impeached President Johnson for violating the Tenure of Office Act.
The members of the United States Congress agreed to impeach President Andrew Jhonson when he tried to fire the Secretary of War, Edward. M. Stanton and wanted to substitute him with General Ulysses. S. Grant. Congress members alleged that Johnson had violated the Tenure of Office Act. Indeed, there were 11 articles of impeachment and the process started on February 24, 1868. Andrew Johnson was the first United States President to be impeached.