2.Why we need both server controls and html controls in asp.net. what is the difference between them?

A.HTML Server Controls:

This controls will follow similar syntax of html client side controls with the same set of properties (with runat="server" attribute). The purpose of this HTML Server controls is towards migration projects. And this HTML Server Controls doesn't support extensibility.

Web Server Controls:

These are very advanced controls if compared to HTML Controls. These controls overcome the extensibility problem which araises in HTML Server Controls. These controls are also called as Smart Controls, because these controls will produce HTML context based on reuested browser.

These Controls also supports data binding and xml based syntax with .net object model.