refer this link
http://www.webblogsforyou.com/100-frequently-asked-interview-questions-on-asp-net-sql-server-oop-concepts/
http://www.webblogsforyou.com/100-frequently-asked-interview-questions-on-asp-net-sql-server-oop-concepts/
add this to the need to check is closed or refreshed !!
<script type="text/javascript">
window.onunload = function (e) {// Firefox || IEe = e || window.event;var y = e.pageY || e.clientY;if (y < 0) {alert("close");}else {alert("refresh");}}
</script>