Edit in JSFiddle

$(document).ready(function(){
    $('#btnGetValue').click(function() {
        var selValue = $('input[name=sample]:checked').attr('id'); 
        $('p').html('<br/>Selected Radio Button ID is : <b>' + selValue + '</b>');
    });
});

<input type="radio" name="sample" ID="rdnNumber1" value="1" /> Number 1<br/>
<input type="radio" name="sample" ID="rdnNumber2" value="2" /> Number 2 <br/>
<input type="radio" name="sample" ID="rdnNumber3" value="3" /> Number 3
<br/>
<br/>
<input type="button" id="btnGetValue" Value="Get Value" />
<p></p>