Use of Apostrophe 's'

Reference: http://www.queens-english-society.com/goodeng2.html

The apostrophe "s" is used for the possessive form of a singular noun - the boy's book; John's ball. In the case of plural nouns ending in "s" an apostrophe is added to the end of the word - the boys' books; the girls' dolls. Where the plural noun does not end in "s" an apostrophe "s" is added, as in the case of a singular noun - the men's cars; women's rights.

In the case of personal names ending in "s" expert opinion seems to vary, although it is generally agreed that "s" should be added whenever possible - Mr Jones's car; Charles's hat - except when the last syllable is pronounced "iz" so that Robert Bridges' poems is acceptable.

In the case of classical names ending in "s" the normal practice is to use an apostrophe at the end - Venus' missing arm; Sophocles' plays.

Personal pronouns - yours, his, hers, theirs, ours - do not require an apostrophe and it should be remembered that it’s is an abbreviation for it is or it has, not the possessive form of it.

Further, who's is an abbreviation for who is or who has, not the possessive form of who - Who's lost his hat? Whose hat is that?

An apostrophe "s" should not be used to denote a simple plural as is becoming common (eg. banana's, disco's, MP's).