Hi rani,
Check this example. Now please take its reference and correct your code.
HTML
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>AngularJS Radio Buttons Validation</title>
    <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.8/angular.min.js"></script>
    <script type="text/javascript">
        var app = angular.module('MyApp', []);
        app.controller('MyController', function ($scope, $window) {
            $scope.Submit = function () {
                if ($scope.SelectedFruit != undefined) {
                    $window.alert('Selected Fruit : ' + $scope.SelectedFruit);
                } else {
                    $window.alert('Please select at-least one Fruit.');
                }
            }
        });
        app.controller('MyController1', function ($scope, $window) {
            $scope.Fruits = [
                                { FruitId: 1, Name: 'Mango' },
                                { FruitId: 2, Name: 'Apple' },
                                { FruitId: 3, Name: 'Banana' },
                                { FruitId: 4, Name: 'Grapes' },
                                { FruitId: 5, Name: 'Orange' }
                            ];
            $scope.Submit = function () {
                if ($scope.SelectedFruitId != undefined) {
                    var fruitName;
                    for (var i = 0; i < $scope.Fruits.length; i++) {
                        if ($scope.Fruits[i].FruitId == $scope.SelectedFruitId) {
                            fruitName = $scope.Fruits[i].Name;
                            break;
                        }
                    }
                    $window.alert("Selected Fruit : " + fruitName);
                } else {
                    $window.alert('Please select at-least one Fruit.');
                }
            }
        });
    </script>
</head>
<body ng-app="MyApp">
    <div ng-controller="MyController">
        <input type="radio" value="Mango" ng-model="SelectedFruit" />Mango<br />
        <input type="radio" value="Apple" ng-model="SelectedFruit" />Apple<br />
        <input type="radio" value="Banana" ng-model="SelectedFruit" />Banana<br />
        <input type="radio" value="Grapes" ng-model="SelectedFruit" />Grapes<br />
        <input type="radio" value="Orange" ng-model="SelectedFruit" />Orange<br />
        <input type="button" id="btnSubmit" value="Submit" ng-click="Submit()" />
    </div>
    <hr />
    <div ng-controller="MyController1">
        <div ng-repeat="fruit in Fruits">
            <label>
                <input type="radio" value="{{fruit.FruitId}}" ng-model="$parent.SelectedFruitId" />
                {{fruit.Name}}
            </label>
        </div>
        <input type="button" id="btnSubmit" value="Submit" ng-click="Submit()" />
    </div>
</body>
</html>
 
Demo