Which tag is neccesary in html 5?

Answer 1

Those you need ^^

If your question expected an answer from between the ones listed as question tag, I guess the expected answer is <!doctype> which isn't a "real" html tag (it's not an html element), even if it's mostly recommanded to use it, but not mandatory :P

Answer 2

@Prakhar Singh:

I have not wrote that <!doctype> must not be used, but that it can be avoided, because it isn't strictly << necessary >>, and that's not strictly an html tag (not html element node). And I wrote also that's << mostly recommanded >> ^^