Hello Surendra,
Here is a small html prototype demonstrating that your code should work.
<!DOCTYPE html>
<html>
<head>
<style type="text/css">
.c1 { padding: 2px 20px 2px 20px; }
</style>
<script src="http://code.jquery.com/jquery-1.9.1.js"></script>
<script type="text/javascript">
$(document).ready(function(){
$('input[type="checkbox"]').each(function () {
$(this).addClass("c1");
});
});
</script>
</head>
<body>
<form name="frmMain" id="frmMain" method="post">
<label>Check 1</label><input type="checkbox" id="chk1" name="chk1"/><span>One</span></br>
<label>Check 2</label><input type="checkbox" id="chk2" name="chk2"/><span>Two</span></br>
</form>
</body>
</html>
What do you mean by not working? May be you don't have proper reference to JQuery script or rule C! itself does not exists or it does not have an attribute which indicate so visually.
Regards,