Option (b) : NaClSoln⟶Na++Cl−
Van't Hoff factor : i=2
Option (c) : Al(NO3)3Soln⟶1Al+3+3NO−3
Van't Hoff factor : i=4
Option (d) : Na2SO4Soln⟶2Na++1SO2−4
Van't Hoff factor : i=3
Only option (a) i.e. Al2(SO4)3 has the same value of Van't Hoff factor as that of K4Fe(CN)6
Option (a) is correct.