JavaScript单选按钮html web表单

I am currently using html to code a 'form entry'. I am also using a JavaScript validation, to validate the input in of the form. At the moment, i have 'name', 'subject' and 'examination number', each working and having functional validations. For the 'qualification' fields, I have radio buttons where the user has to click-select their qualification. I have the validation in place, but unfortunately I cant get the field to be highlighted in red and display the error message when the form is submitted and the 'qualification' has been left blank. everything works apart from the qualification field. It would be great if someone could fix the validation of the 'qualification' so that when the field is left emty, the text will be highlighted and the error message will be included. thanksI am currently using html to code a 'form entry