Dropdown SelectedIndex Item in MVC Application

I have created in the Dropdown list in the MVC Application.Also I have get the value from by giving thru the function.  Question is: If i select the 1st item from the Dropdown menu from the list, i do not want to display the label control in the form. If i select the 2 option from the Dropdown i want to display the Label Control
So i have to write the SelectIndex Method in the application. Please tell me how to write the SelectedIndex Method in the MVC application?
In the Form I have written AddRule.aspx
<%= Html.DropDownList("gs1")%>
In the Controller
ViewData["gs1"] = new List<SelectListItem>
{
new SelectListItem
{
Text = "Select",
Value = "0",
Selected = false
},
new SelectListItem
{
Text = "(",
Value = "1",
},
new SelectListItem
{
Text = ")",
Value = "2",
}
};
In the Model,
[Required]
[DataType(DataType.Text)]
public IEnumerable<SelectListItem> gs1 { get; set; }