What president was impeached for firing secretary of state?

Answer 1

There was no President of the United States that was impeached for firing his Secretary of State.

Perhaps you mean Andrew Johnson, the 17th President of the United States from 1865-1869, who was impeached for removing Edward Stanton, the Secretary of War. This violated a recently passed law, the Tenure of Office Act, which stated that the President couldn't remove cabinet members from their positions. The law was also quite unconstitutional, and was passed for the sole purpose of finding a reason to impeach Johnson, who was unpopular with the Republican Party.

Although Johnson was impeached, he was later acquitted, and retained the office of the presidency until the next election cycle, when he chose not to run.