If a singular noun ends in an "s," use "'s" to create the possessive form only if the noun ends in a "s" sound. However, if the noun ends in a "z" sound, use just an apostrophe without adding an additional "s." This produces a more pronounceable possessive.

How do you know which possessive pronoun to use?

Possessive pronouns can be used to describe single objects or more than one. To describing something singular, you would use one of the following pronouns: “mine, yours, his, hers”. E.g. “The cat is mine.” “ This round is yours.

Is it Chris's or Chris '?

In other style guides, Chris takes an apostrophe and an s: Chris's. "AP" rules that proper names such as Chris, Agnes, and Russ take only an apostrophe, like these examples: Chris' photograph appears on page 1 of the business section. (Other style guides use Chris's.)