Which has the lowest freezing point? a. pure water b. 1.0 m nacl c. 1.0 m k3po4 d. 1.0 m cacl2 e. 1.0 m glucose (c6h12o6)?

Freezing point depression depends of the number of particles of the solute in the solution.
1)Pure water have highest freezing point. All other solutions with given solutes will have lower temperatures. 
2) The more particles of the solute in the solution the lower freezing point is going to be.
b. 1.0 m NaCl ( dissociates and give 2 mol ions (1 mol Na⁺ and 1 mol Cl⁻))
c. 1.0 m K3PO4 (dissociates and give 4 mol ions (3 mol K⁺ and 1 mol PO4³⁻)
d. 1.0 m CaCl2 (dissociates and give 3 mol ions (1 mol Ca²⁺ and 2 mol Cl⁻))
e. 1.0 m glucose (c6h12o6) (glucose does not dissociate, and solution have
1 mole of particles of the solute(glucose))

The largest number of particles has 1.0 m K3PO4  solution, and it is has lowest freezing point . Answer is C.