P is ammonium iron(II) sulfate — Fe²⁺, NH₄⁺, SO₄²⁻. NaOH → green ppt insoluble in excess (Fe²⁺) + ammonia on warming (NH₄⁺); barium nitrate → white ppt (SO₄²⁻).
Purple KMnO₄ (Q) oxidises Fe²⁺ to Fe³⁺:
5Fe²⁺ + MnO₄⁻ + 8H⁺ → 5Fe³⁺ + Mn²⁺ + 4H₂O
That equation is where the 5 : 1 ratio used in (g)(i) comes from. The titration is self-indicating — the first persistent pale pink is the end-point. Read the burette from the top of the meniscus. Average titre 13.65 cm³ → 2.73×10⁻⁴ mol KMnO₄ → ×5 → 1.365×10⁻³ mol Fe²⁺ → 0.0546 mol/dm³.
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