one/ones

Adjective of quality can be used without their nouns if the pronoun one/ones is placed afterwards.
Mostly used with an idea of selection or comparison:

• I like those pencils: I’ll take a blue one.
• Small bananas are often better than big ones.

One is often omitted after the + superlative and sometimes after the + comparative, and after adjectives of colour:

• I took the largest (one)
• I bought the more expensive (one) of the two.
• Which do you like? I like the blue (one)

One is pronoun equivalent of a/an

• Did you get a ticket? Yes, I managed to get one.

The plural of one used in this way is some:

• Did you buy grapes? Yes, I bought some > Sì ne ho comprata [quantità imprecisata; a certain number or amount]

Contrast with:

• Did you hear the speech? Yes I heard it >> Si l’ho ascoltato
• Did you hear the speeches? Yes, I heard them.

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no /none
No (adjective) and none (pronoun) can be used with affirmative verbs to express a negative: they are alternative to negative verb + any.

• I have no apples > I have not any apples
• Tom has none > Tom hasn’t any
• I took no photos > I didn’t take any photos.

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Pronouns and possessive adjectives with someone, somebody, anyone, anybody, no one, nobody

All these expressions have a singular meaning and take a singular verb:

• Someone wants to speak to you on the phone

Personal pronouns should logically be singular too (he/she > his/her). Whenever the gender is in doubt we generally use they and their instead:

• No one saw Tom go out, did they?
• Has anyone left their luggage on the train?

Something, anything and nothing has no problem of gender, so we use it:

• Something went wrong, did it?