First comming to answer the question of Kumud,
Since you are in the no-archive mode you can only do offline drop and not offline immediate.

Now comming to answer the question of Gayathri, Since the database is not in the archive mode, point in time recovery is not feasible. So to resolve this issue, things that can be done are

Code:
   Mount the database
   
   alter database datafile '/../filename' offline;

   alter database open;
  
   restore the backup copies of the damaged datafile 

   recover tablespace tablespace_name;

   alter tablespace tablespace_name online;
I hope this would answer your question.

Sam