Hi @sajidakeel
That field probably render HTML tags only, but a workaround, if you are used dealing with hard code then you might use child theme and enable your adsense script in a custom mode (and not loosing it when update your OJS version).
Look this thread to see how do it:
Then edit templates/frontend/components/footer.tpl
file and insert your adsense script after (or before) this line (number only to location), or whatever you want in file:
35: {$pageFooter}
Israel Cefrin
Public Knowledge Project Team