Whenever you add any HTML tags in side a blog post, they wont be displayed in the post once published. It is because, the all the post content will be published as encryption and it can not understand the HTML tags. So to add HTML tags, the content should be made understood by the encryption. This can be done by any adsense code converter to change the tags to the equivalent encrypted text. I normally use eBlogger for this and here is the link.
If you have any questions, please leave them in the comments.