Explain how Viewstate is being formed and how it is keeps on client.
The type of ViewState is System.Web.UI.StateBag, which is a dictionary that keeps name/value pairs. View State is persisted to a string variable by the ASP.NET page framework and sent to the client and back as a hidden variable. Upon postback, the page framework parses the input string from the hidden variable and populates the ViewState property of every control. If a control uses ViewState for property data instead of a private field, that property automatically will be persisted across round trips to the client. (If a property is not persisted in ViewState, it is good practice to return its default value on postback.)