The possessive case (and more generally speaking, the genitive case) of any singular noun in English is formed by adding an apostrophe followed by the letter "s" no matter how the modified word is spelled: Thus the possessive form of business is business's.
* Exceptions to this rule are biblical polysyllabic names ending in a sibilant, with Jesus' and Moses' either listed as the common examples or as the only permitted ones. Some contemporary sources incorrectly expand this exception to any polysyllabic notable name ending in a sibilant ("Dickens' novels").
Actually, many modern style guides allow the use of only an apostrophe after words that end in S. It isn't necessarily incorrect. It just depends on which style guide you are required to use.
Possessive of the singular business is business's; possessive of the plural businesses is businesses'.
The singular possessive is business's. The plural possessive is businesses'.
The singular possessive is fish's.
Buzz's is the singular possessive.
The possessive form is Amos's.
Possessive of the singular business is business's; possessive of the plural businesses is businesses'.
The singular possessive is business's. The plural possessive is businesses'.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
The singular possessive of "ant" is "ant's" and the plural possessive is "ants'".
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive pronouns are "my," "mine," "your," "yours," "his," "her," and "its."
The singular possessive of dish is dish's
The possessive form of the noun businesswoman is businesswoman's.example: A businesswoman's day doesn't end at the end of a business day.
The singular possessive is Martin's.
The singular possessive is fish's.
Grave's is the singular possessive.
The singular possessive form of "test" is "test's".