Unusually, nothing is hidden this year: W is hydrogen peroxide (colourless), X is aqueous potassium iodide (colourless) and Y is aqueous potassium manganate(VII) (purple). The deductions are about the ROLE hydrogen peroxide plays — oxidising or reducing agent — in each test.
The purple is decolourised at first, then a brown-black solid (MnO₂) forms and settles, with effervescence of oxygen; the tube feels warm.
Each portion turns the mixture purple, then the purple fades to colourless (MnO₄⁻ → colourless Mn²⁺) with tiny bubbles of oxygen. Each successive portion fades faster — the Mn²⁺ produced catalyses the reaction. Here the H₂O₂ is the reducing agent.
The H₂O₂ oxidises iodide to iodine: colourless → yellow → reddish-brown, and black solids settle. There is NO effervescence in this test. Here the H₂O₂ is the oxidising agent.
The iodide catalyses the decomposition of the hydrogen peroxide — effervescence of oxygen; the solution turns pale yellow (the TYS says "remains colourless" — both are accepted).
Oxygen relights a glowing splint: light the splint at the Bunsen, click it to blow the flame out (the tip keeps glowing), then hold the glowing tip at the tube mouth. A lighted splint is the wrong test — the examiner flagged it.