Hi Mahesh,
HtmlCode for First page from where query string is being set
<asp:LinkButton ID="lnkTest" runat="server" PostBackUrl="~/AlphabetValidation.aspx?A=1"
Text="Click Me"></asp:LinkButton>
HtmlCode for page where this value will be accessed
<asp:Label ID="lblTestText" runat="server"></asp:Label>
Code
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
lblTest.Text = Request.QueryString("A")
End Sub