SEO backlinks correct format

I am confused about the correct format for a backlink URL that is whether it should end with / or not. Whether a http is needed. Which among the following is the correct format.

<a href="Keyword Here">http://www.example.com</a>

<a href="Keyword Here">http://www.example.com/</a>

<a href="Keyword Here">www.example.com</a>

Thanks in advance!

 

<a href="http://www.domain.com">keyword here</a>

 

Thanks. Looks like I even forgot how to write a correct URL.

 

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