Here is a little code to find and click the first radio button in a set using Selenium:

var didYouGraduateRadioButtonName = string.Format("{0}{1}{2}", "rb_Graduated[", indexValueToUse, "]");
           
 var rbDidYouGraduate = driver.FindElement(By.Id(didYouGraduateRadioButtonName));
            
javaScriptExecutor.ExecuteScript("arguments[0].checked = true;", rbDidYouGraduate);