Which solution containing 1 mole of solute dissolved in 1000 grams of water has the lowest freezing point?

You can figure out the answer to the question without doing many calculations (even though no options are provided). Freezing point depression is a colligative property, meaning it's related to the AMOUNT of solute rather than the IDENTITY of the solute.

If all solutions contain 1 mole of a solute that DOESN'T dissociate in the same amount of water, the freezing point will be decreased by the same amount in all of them.

If you are given solutes that DO dissociate, the solution with the lowest freezing point will be the one containing solutes that dissociate into the most particles.

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom. 

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