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 Y loses its colour and a brown-black solid (MnO₂) forms and settles, with effervescence of oxygen (it relights a glowing splint); the test-tube becomes hotter.
Adding the acid: no observable change. The first 5 drops of Y turn the colourless solution pink; within about a minute the pink fades to colourless (MnO₄⁻ → colourless Mn²⁺) with tiny bubbles of oxygen. Each later portion is decolourised faster — the Mn²⁺ produced catalyses the reaction. Here the H₂O₂ is the reducing agent.
The H₂O₂ oxidises iodide to iodine: the colourless solution turns yellow, then a brown solution, and a black solid settles. There is NO effervescence, and the solution never becomes colourless. Here the H₂O₂ is the oxidising agent.
The iodide catalyses the decomposition of the hydrogen peroxide — effervescence of oxygen (it relights a glowing splint); the colourless solution turns yellow, and the test-tube becomes warm.
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.