For 1 molal solution of each compound maximum freezing point will be assuming compete ionisation in each case :

Options

A. `[Fe(H_(2)O)_(6)]Cl_(3)`
B. `[Fe(H_(2)O)_(5)]Cl]Cl_(2).H_(2)O`
C. `[Fe(H_(2)O)_(4)Cl_(2)]Cl.2H_(2)O`
D. `[Fe(H_(2)O)_(3)Cl_(3)].3H_(2)O`

Answer

4

Explanation

In 4 option there is no ionisation
`DeltaT_(f)prop i^(@)`
`F.P.=0-DeltaT_(f)`
Hence greater the value of `DeltaT_(P)` smaller the F.P. hence maximum freezing point if of `'4'` option.