change code like this
<asp:RadioButtonList ID="RadioButtonList1" AutoPostBack="true" runat="server"
RepeatDirection="Horizontal" OnSelectedIndexChanged="RadioButtonList1_SelectedIndexChanged">
<asp:ListItem>Fixed</asp:ListItem>
<asp:ListItem>Variable</asp:ListItem>
<asp:ListItem>Expenses Covered</asp:ListItem>
<asp:ListItem >No Stipend</asp:ListItem>
</asp:RadioButtonList>
in cs page add following
protected void RadioButtonList1_SelectedIndexChanged(object sender, EventArgs e)
{
if (RadioButtonList1.SelectedItem.Text == "No Stipend")
{
}
}