1.What is the major difference between Ado and Ado.net?
The main difference is the possibility to work disconnected. This option is achieve using dataset with which you can navigate back and forth through rows.

2.When doing an ExecuteScalar method on a Command object, if the querry attached return more than one column will the call fail?
No the call will not fail, the value of the first column will be return.

3.What data types do the RangeValidator control support?
Integer, String, and Date.