What is pseudo columns ? Name them? - oracle

What is pseudo columns ? Name them? 
A pseudocolumn behaves like a table column, but is not actually stored in the table. You can select from pseudocolumns, but you cannot insert, update, or delete their values. This section describes these pseudocolumns:
* CURRVAL
* NEXTVAL
* LEVEL
* ROWID
* ROWNUM

How many columns can table have? 
The number of columns in a table can range from 1 to 254.

Is space acquired in blocks or extents ? 
In extents .

What is clustered index? 
In an indexed cluster, rows are stored together based on their cluster key values . Can not applied for HASH.

What are the datatypes supported By oracle (INTERNAL)? 
Varchar2, Number,Char , MLSLABEL.

What are attributes of cursor? 
%FOUND , %NOTFOUND , %ISOPEN,%ROWCOUNT

Can you use select in FROM clause of SQL select ? 
Yes.