An acid can be defined as a proton donor.
No, they can have potential energy
I think that different liquids have different freezing points because every liquid consists of different atoms and different things that make up the atom causing them to have different freezing points.
6.02 x 10^23 is Alvogrado's number (Amedio Alvogrado is the name). This formula is determined to find the amount of particles within a substance by a mole.
I hope this helps!