“I’ve always had a problem with #6. I understand the use of the apostrophe for the contraction of “it is” - but the non-use of it when dealing with possession has always puzzled me.”
An easy way to remember it is to think of an apostrophe as a missing letter. In “It’s” the apostrophe stands for the missing ‘i.’ If you say, “The dog licked it’s tail,’ you’re actually saying ‘The dog licked it is tail.”
“An easy way to remember it is to think of an apostrophe as a missing letter.”
Unless it’s a possessive.
English is an exceptional language - there are more exceptions to most of its rules than followers of the rules.