The word Neutrogena is a singular, proper noun; the name of a product, a registered trademark of the Neutrogena Corporation. There is no plural form for this noun; multiple units are expressed in 'bottles of', 'jars of', 'tubes of', etc.
Yes. Hay is a singular noun. A Singular noun means one item only. So technically, hay is a singular noun.
The noun 'theory' is a singular noun. The plural noun is 'theories'.
The noun 'mice' is the plural form of the singular noun 'mouse'.
Yes the word question is a singular noun. The plural noun is questions.
The noun mailbox is the singular form; the plural is mailboxes.
The noun 'fun' is a singular non-count noun, it has no plural form.
An example of a singular noun for a school could be "institution."
The noun juggler is a singular noun. The plural noun is jugglers.
Feet is a plural noun. Foot is a singular noun.
The noun family is the singular form; the plural form is families.
The singular noun is "louse" and the plural noun is "lice."
"Children" is a plural noun. The singular form is "child."