W = HCl + HNO₃. Silver nitrate → white ppt (chloride → HCl); barium nitrate → no change (no sulfate); NaOH + aluminium foil, warmed → ammonia (damp red litmus → blue) → nitrate → HNO₃.
X (acidified FeCl₃) + Y (KI) → iodine; starch → blue-black; thiosulfate delays it. More X → faster. Rate = 1000/time, no graph. Ratio = rate 2 ÷ rate 1.
Written observations are checked offline against the mark scheme's points; the calculations are marked numerically (with tolerance). The feedback tells you what's missing so you can re-mark.