My questuion about the space that reserved by null value in Oracle 10g ?
There is this wonderful tool called tahiti.oracle.com. It contains all of the documentation that you should need. In fact I was able to find out about nulls is about 30 seconds. You should avail yourself of all of the resources out there.
And quit starting second threads like "I'm waiting." As people volunteer their time, there should be no expectation of urgency on getting any kind of response.