Except / Except for

  1. Except this mistake, you did very well.
    1a. Except for this mistake, you did very well.
    1b. You did very well except this mistake.
    1c. You did very well except for this mistake.
  2. Except the bedroom, he cleaned all the rooms.
    2a. Except for the bedroom, he cleaned all the rooms.
    2b. He cleaned all the rooms except the bedroom.
    2c. He cleaned all the rooms except for the bedroom.
  3. Except Raman and Sita, nobody was invited.
    3a. Except for Raman and Sita, nobody was invited.
    3b. Nobody was invited except Raman and Sita.
    3c. Nobody was invited except for Raman and Sita.
    Please correct all.
    Thanks.

1a, 1c, 2a, 2b, 2c, 3a, 3b, 3c are all correct forms.