Why the l in front of on in last sentence

Bonjour Chris,

To supplement on Chris's excellent answer: 'l' is used with 'on' for reasons of euphony. It is very common to use it in written French and therefore its usage is rather formal. You usually find it after 'lorsque, puisque, quoique' or after 'et, ou, où, qui, quoi, si' (here to avoid pronouncing two vowel sounds one after the other).

See link here: on-vs-l-on

I hope this is helpful.

Bonne journée !