Why is its the exception to the 's rule in English grammar?
Because if we used "it's" for possession, we'd become confused
whether this were used to show possession or to show a contraction
of the two words "it" and "is."
There probably aren't any. An apostrophe is a "punctuation mark"
and not a noun (like car) or a verb (like to jump) or an adjective
(like happy). Punctuation marks usually do not have synonyms. An
apostrophe is something you use in grammar to show possession or
ownership. John's book. Mary's house. There is no other word for
"apostrophe", and no other way to show possession other than using
that punctuation mark.
How do these words show possession Mr Happiness angel?