why all of these <br> <\br> and <br /> all works exactly same during html coding

Answer 1

br tag syntax will work in HTML files whether it be in <br> </br> or <br/> because br tag is compatible with all in HTML format and since its a empty hTML tag requires no closing tag.
But XML(Extensible Mark up Language) requires br tag to have a closing tag and depending on br tag used output will be given.

Answer 2

All tags in XML must have a closing tag as a condition compared to HTML which doesnt require br to have closing tag.

Answer 3

it means that there is no difference between the two as far as HTML is concerned and what differences are there in case of XML please give an example