Hi Tom,
a) I would like to know how the one block is created in free list as normally after deletion it goes into free list.

SQL> create table t ( x int, y char(2000) default '*' )
  2  storage ( initial 40k next 40k minextents 5 )
  3  tablespace system;

Table created.

SQL> insert into t (x) values ( 1 );

1 row created.

SQL> analyze table t compute statistics;

Table analyzed.

SQL> compute sum of blocks on report
SQL> break on report
SQL> select extent_id, bytes, blocks
  2  from user_extents
  3  where segment_name = 'T'
  4  and segment_type = 'TABLE';

 EXTENT_ID      BYTES     BLOCKS
---------- ---------- ----------
         2      61440         15
         3     102400         25
         4     143360         35
         0      40960         10
         1      40960         10
                      ----------
sum                           95

SQL>  clear breaks
breaks cleared
SQL> select blocks, empty_blocks, avg_space, num_freelist_blocks
  2  from user_tables
  3  where table_name = 'T';

    BLOCKS EMPTY_BLOCKS  AVG_SPACE NUM_FREELIST_BLOCKS
---------- ------------ ---------- -------------------
         1           93       1971                   1

b) In one of your followup you have mentioned the first block of each table is used by the system. So it means
totally 96 blocks are allocated to this table?

c) Your solution
(an insert of a new row that finds the freelists empty will 
get some blocks from beyond the HWM and put them on the freelist if the new row does not exceed the pctfree)
Can you please explain - put them on the freelist if the new row does not exceed the pctfree -

Thanks.