Singular forms and possessive forms are terms for nouns and pronouns.
The word 'not' is an adverb, a word used to modify a verb, an adjective, or another adverb. Examples:
modifies a verb: This is not a good day.
modifies an adjective: He is not my boyfriend.
modifies an adverb: We are moving but not very far.
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
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'.
The singular possessive of criteria is criteria's.
There's no such thing as a singular possessive verb. Chris's is a singular possessive noun.