All i write in my code are Right. and it will give desired output.and my revised code is below.
DataTable dt = obj.FetchAllPerson();
List<string> ids = new List<string>();
for (int i = 0; i < dt.Rows.Count; i++)
{
ids.Add(dt.Rows[i][0].ToString());
}
DdlDelete.DataSource = ids;
DdlDelete.DataBind();
ListItem item = new ListItem("-Select ID-", "0");
DdlDelete.Items.Insert(0, item);