Chapter 22 - Section 22.1 - Coordination Compounds - Checkpoint - Page 990: 22.1.2

d) Potassium hexafluoroferrate(III) is the correct answer

same as the above question using IUPAC rules for naming the compound we can easily solve this one also here , the potassium metal is outside having the cationic par so we will write its name first then the anion name which is $[FeF6]^{-3}$ we will add -ate at the end because it is having the anionic part its name would be $hexafluoroferrate(III)$ so correct answer is (d) d) $Potassium\space hexafluoroferrate(III)$