15. In Oracle can we do any DMLs in a function which is called from a select statement?

No. Oracle Throws Error
      ORA-14551: cannot perform a DML operation inside a query
      ORA-06512: at "EMP.FNC_VACATION_UPDATE", line 11

16. In Oracle, what happens if there is no statement inside an Anonymous block?

For Eg:
Declare
Begin
End;
         Ans: It will throw Error.

Correct:
        Declare
        Begin
        NULL;
        End;