What is the Default value that is what is the default value set for precision and scale in a column defined as NUMBER. Anyone have idea on this?

The datatype in a declaration can either be constrained or unconstrained. A datatype is constrained when you specify a number which constrains or restricts the magnitude of the value which can be assigned to that variable. A datatype is unconstrained when there are no such restrictions.

And the datatype NUMBER. It supports up to 38 digits of precision -- and uses up the memory needed for all those digits. If your variable does not require this much memory, you could declare a number with a constraint, such as the following:

a NUMBER(1);

b NUMBER(20,5);
Constrained variables require less memory than unconstrained number declarations like this:

c_no_limits_here NUMBER;

But could you specify what is the default value set for precision and scale in a column defined as NUMBER.