[INeedSerotonin]

Hello. I just began studying polymers, and I was given this exercise that asks me to mark the option with monomers that produce polyester and polypropylene.

The polypropylene is actually very easy, but my problem is with the polyester. Isn't a polyester made from an acid and an alcohol--for example, terephthalic acid and ethylene-glycol? Then what even is that on option (C)? That doesn't look like an acid to me; that looks like an ester.

Could you guys please explain it to me?

Thanks

EDIT: perhaps I confused myself with the meaning of "monomer"  but I'm still confused with the formula. So I have to get the monomer and take out one OH and one H from the opposite side? Where does the other "ethylene-glycol" part go???!?!?! 

I searched the internet and found this:

[AWK]

Bis(hydroxyethyl) terephthalate (BHET) is one of the starting materials for poly(ethylene terephthalate) (PET) synthesis.

[INeedSerotonin]

Bis(hydroxyethyl) terephthalate (BHET) is one of the starting materials for poly(ethylene terephthalate) (PET) synthesis.

Ahhh I think I got it now: a polyester is a group of compounds!

Thanks

[INeedSerotonin]

Let me ask you one more thing:

I've learnt that this reaction liberates H₂O. Some sources say that it is (2n) H₂O; others say only (n) H₂O; and others, still, say (n-1) H₂O. Why is that?

[AWK]

From this reagent, for each molecule, the one molecule of ethylene glycol is liberated during catalytic condensation.