Answer is 5.0 mol.
Explanation;
The balanced reaction between KMnO₄ and HI is
2KMnO₄ + 10HI + 3H₂SO₄ → 2MnSO₄ + K₂SO₄ + 5I₂ + 8H₂O
The stoichiometric ratio between HI and I₂ is 2 :1.
Hence, moles of HI needed = moles of 5I₂ produced x 2
= 2.5 mol x 2
= 5.0 mol