There are two options how to add the AdSense activation code into header of your website. The one is the coding option, the other one is to use a plugin which injects the ad code into your site. I will introduce both options to you:
The most simple option is to use a separate plugin which allows you to add extra code into the head of your website. You can install the plugin from the link below:
WPCode – Insert Headers and Footers + Custom Code Snippets – WordPress Code Manager
You can use it to put any code into the header or even footer of your website:
The manual way of adding the AdSense activation code into header of your website is to open your WordPress theme template files header.php and than copy the AdSense activation code directly just before the closing </head>
like so:
<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> <script> (adsbygoogle = window.adsbygoogle || []).push({ google_ad_client: "ca-pub-9796982316463600", enable_page_level_ads: true }); </script>