@shijitht

Go Invisible option in pidgin is an option only. It will set status to busy. But there is a solution for it.

Go online.
Enable the XMPP console in Tools > Plugins.
Now select Tools->XMMP Console->XMMP Console.
Check your gmail account is selected in the console.
Put these code in the second box and hit enter.
Don’t mind the trail of code in the monitor, but a hacker could find it pretty useful.

{{{
<presence>
<priority>5</priority>
</presence>
<presence type="unavailable">
<priority>5</priority>
</presence>
}}}

Now go invisible.
To reset change unavailable to available and put it in the console.
For more go to http://www.madhusudancs.info/invisible.