In Fig. 3, a piece of damp iron wool was placed in a measuring cylinder containing 50cm³ of air as shown in the diagram labelled A. Diagram B shows the apparatus one week later. Complete the table of results below. Volume of gas in A, Volume of gas in B. Use the results to calculate the percentage decrease in the volume of gas in the measuring cylinder after one week.

a) i) To complete the table, we read the volumes from the diagrams. In Fig. 3, Diagram A shows the initial setup. The measuring cylinder contains 50 cm$^3$ of air. In Fig. 3, Diagram B shows the setup one week later. The water level has risen to the 10 cm$^3$ mark, indicating that 10 cm$^3$ of gas remains.

| | | |---|---| | Volume of gas in A | 50 cm$^3$ | | Volume of gas in B | 10 cm$^3$ |

ii) Step 1: Determine the initial and final volumes of gas. Initial volume of gas (from A) $= 50 cm^3$ Final volume of gas (from B) $= 10 cm^3$

Step 2: Calculate the decrease in volume. Decrease in volume $= Initial volume - \text{Final volume}$ $= 50 cm^3 - 10 cm^3 = 40 cm^3$

Step 3: Calculate the percentage decrease in volume. Percentage decrease $= \frac{Decrease in volume}{Initial volume} \times 100\%$ $= \frac{40 cm^3}{50 cm^3} \times 100\%$ $= \frac{4}{5} \times 100\%$ $= 0.8 \times 100\%$ $= 80\%$ The percentage decrease in the volume of gas in the measuring cylinder after one week is \boxed{80%}.