- J’ai vu un_avion (mandatory liaison)
- L’avion était_énorme (optional liaison)
- J’ai vu l’avion énorme (impossible liaison)
- C’était mon_avion favori (mandatory liaison)
And we could even have had :
- J’ai vu un_énorme avion (mandatory liaison)
I couldn’t sum up the rules behind it with clarity because, as a native speaker, I’m largely resorting on intuition and sounding right, thus making me a poor explainer here. Which is not that much of a trouble, since there are many online sources :
Some could be :
The sentence in which there is the less liaison is the third one: there is in it actually none. One should say:
- J’ai vu un-n-avion;
- L’avion était-t-énorme;
- C’était mon-n-avion.
In French a liaison is usually done with the word mon when it is followed by a vowel.
Those two are probably always done.
J’ai vu un avion
C’était mon avion favori
I think this one will be done less often.
L’avion était énorme
This one will almost never be done:
J’ai vu l’avion énorme
probably because the standard place for the adjective here is before the name, like this:
J’ai vu l’énorme avion.
and putting it after will be done for emphasis, probably followed by other adjectives, and emphasis is something which break the liaison. (BTW, in the standard sentence, there will be a liaison between énorme and avion).