Is there a way to know how many elements have close tags and which one doesn't? Any links to refer pls?

Answer 1

tag has starting and closing tag if line between the tag can go from one word multiple lines .
eg: <p></p> para tag

tag which is specific and use for special function generally doesn't have end tag.
eg: <img> since img tag is use to embed image and it's roles ends there.

for further reference you can refer w3schools.com