Four species are listed below i. $\mathrm{HCO}_3^{-}$ ii. $\mathrm{H}_3 \mathrm{O}^{+}$ iii. $\mathrm{HSO}_4^{-}$ iv. $\mathrm{HSO}_3 \mathrm{~F}$ Which one of the following is the correct sequence of their acid strength?

• A

  iv $ < $ ii $ < $ iii $ < $ i
• B

  ii $ < $ iii $ < i < $ iv
• Correct answer
  C

  i $ < $ iii $ < $ ii $ < $ iv
• D

  iii $ < $ i $ < $ iv $ < $ ii

Hence, the correct answer is option: 'C'.