ngIf

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/angular.js/1.3.14/angular.js"></script>
<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.4/css/bootstrap.css">
<div ng-app="demoApp" ng-controller="DemoController">
    <ul class="list-group" data-toggle="items" ng-repeat="ques in questions">
        <li class="list-group-item">
            <input type="checkbox" />{{ques.question}} 
            <div ng-if="ques.description">
                <i class="glyphicon glyphicon-question-sign" title="{{ques.description}}"></i>
            </div>

        </li>
    </ul>
</div>

JavaScript

var demoApp = angular.module('demoApp', []);

demoApp.controller('DemoController', function ($scope) {

    $scope.questions = [{
        question: 'lskdhblsdl',
        description: 'jsbdjbds'
    }, {
        question: 'sdgffddl',
        description: null
    }, {
        question: 'dfgdfgdfgdf',
        description: 'jsbdjbds'
    }, {
        question: 'dfgdfgdf'
    }, {
        question: 'dfgfdgdfg',
        description: 'jsbdjbds'
    }];


});