1.HTML was designed to display data with focus on how data looks while XML was designed to be a software and hardware independent tool used to transport and store data, with focus on what data is.
2.HTML is a markup language itself while XML provides a framework for defining markup languages.
3.HTML is a presentation language while XML is neither a programming language nor a presentation language.
4.HTML is case insensitive while XML is case sensitive.
5.HTML is used for designing a web-page to be rendered on the client side while XML is used basically to transport data between the application and the database.
6.HTML has it own predefined tags while what makes XML flexible is that custom tags can be defined and the tags are invented by the author of the XML document.
7.HTML is not strict if the user does not use the closing tags but XML makes it mandatory for the user the close each tag that has been used.
8.HTML does not preserve white space while XML does.
9.HTML is about displaying data,hence static but XML is about carrying information,hence dynamic.
Thus,it can be said that HTML and XML are not competitors but rather complement to each other
and clearly serving altogether different purposes.