First, we'll identify the beaker containing pure water as follows:
We'll take equal masses from each of the three beakers and measure the mass of each.
We'll then identify the density of each by using the rule : density =mass/volume
Pure water will be the liquid having density equal to 1 gm/cm^3
Then, we'll differentiate between the salt and sugar solution by measuring the conductivity of each solution. Salt solution is a good conductor while solution of sugar is a bad conductor.
I believe it would be compound.
Technically, no because you are not changing the chemical make up of water when you freeze it, you are only changing the state. (liquid to solid)