put in decreasing freezing point 0.10m Na3PO4,0.35m NaCl,0.20 m MgCl2, 0.15 m C6H12O6,0.15 m CH3COOH

Answer 1

delta T = i*Kf*m
Since Kf is a constant you may ignore it and multiply i*m. The largest number will be the largest delta T.

Answer 2

Arrenge Na3PO4 m, 0.35 m NaCl,0.2m MgCl2m,0.15m C6H12O6 m, 0.15CH3COOH m in decreasing order of their expected freezing point