The correct answer is (c).
Good faith within the meaning of the Indian Penal Code (IPC) means an act in fact done honestly. It is a subjective test, i.e., it depends on the intention of the person doing the act. If the person believes that he is acting honestly, then he will be considered to have acted in good faith, even if his belief is wrong.
The other options are incorrect because they are objective tests. For example, (a) an act done with due care and attention is not necessarily an act done in good faith. A person may act with due care and attention, but still have a dishonest intention. Similarly, (b) an actual belief that the act done is not contrary to law is not necessarily an act done in good faith. A person may believe that his act is not contrary to law, but still have a dishonest intention. Finally, (d) an act done under bonafide belief is not necessarily an act done in good faith. A person may act under bonafide belief, but still have a dishonest intention.
In conclusion, the correct answer is (c). Good faith within the meaning of the IPC means an act in fact done honestly.