The possessive form of the singular noun Maddox is Maddox's.
Example: We bought the vegetables at Maddox's farm.
The singular possessive is Maddox's. The plural possessive would only be used if there was a group of people all having the name Maddox, which would be Maddoxes'.
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 mine, yours, his, hers, and its. The singular possessive adjectives are my, your, his, her, and its.
The singular possessive of dish is dish's
The singular possessive is Martin's.
The singular possessive is fish's.
Grave's is the singular possessive.
The singular possessive is test's.
Buzz's is the singular possessive.
The singular possessive is biker's; the plural possessive is bikers'.