Ain't nobody else gonna touch my lemon! I'ts MINE! Gimme a lingot if you would touch it.
Why do you pronounce the t in "c'est" when you it is followed by un but not when it's followed by mon?
In French, they don't like a word to start with a vowel, so that word borrows the last consonant letter of the word in front of it. This is called "liason".
the phenomenon is called 'liaison'. Wikipedia has an extensive (perhaps unnecessarily-extensive) article at https://en.wikipedia.org/wiki/Liaison_%28French%29
Why can't you just say C'est ma citron? What is the difference between both of them?
Use 'ma' when the object possessed is (grammatically) feminine.
Use 'mon' when the object is (grammatically) masculine, or begins with 'a'.
Thus 'mon citron' (masc) et 'ma pomme' (fem), mais 'mon aimee' (female friend, but ma + a… => mon )