How Do You Know What Molecules have the LOWERS FREEING POINT

Like if a question were to say something like

"WHich one has the lowest freezing point"
A. NaCl
B. CoCl3
C. FeCl3


or something like that ( I do not know the question accurately)

How can you determine that???

It is a colligative property. So that means it is a property of a compound, not the specific compound.

And in your case, how many ions forms in water? The more ions, the lower the freezing point.

So, NaCl forms two ions in solution.

So your problem is, do both B and C completely ionize, or not?

If you had Na3(PO4), you would get four ions.