1.explain SOAP?2.Explain AutoPostBack?3.explain types of Authentication?

SOAP is a data transfer protocol. XML web service use SOAP to
transfer the web service
Soap is one kind of starndard for web service. soap is Simple
Object Access Protocol. If th method of web service is soap then
the communication is done by message  passing between server and client.

soap is sipmle object access protocol is using in the transfer protocol
SOAP(simple object access protocol)mainly used in web services.
Autopostback will automatically postback to server when the list
selection changes.Types of authentication:Windows,form,passport,none 



If AutoPostBack=true means automatically request will go to server you will
select any content from drop down list control ,list box etc.
Authentication :Authentication is process to check the user
credentials Against database,xml etc.