Syntax of open- tag with attributes

Question

why we don't use in open tag the / symbol?
e.x.
<p align="center" /> instead of
<p align="center">
?

Answer 1

HTML is quite tollerant, it accept even mistakes, but the rigth syntax is with / at the beginning of the closing tag for paragraphs.

Answer 2

<p align="center">ciao</p>