I am a single parent child. In none of my documents my father name appears. Only my mother name appears where provision is there. Hence where father/guardian is written can I write my maternal grand father name with whom we stay.
If the form in not asking about your father name you don't need to mention that as those children who are separated from either of the parents and living in the custody of either of the parents, and in whose case mother or father has been declared as a legal guardian by a court of law.so as per this law you can write your mother name at the place where they ask about guardian name.
Hope it helps..