Four agar blocks are coloured green with universal indicator and placed in $1\ \text{mol dm}^{-3}$ hydrochloric acid. The length of time needed for the agar blocks to turn from green to red was measured. Which agar block would turn completely red first?
- A$2\ \text{cm} \times 2\ \text{cm} \times 2\ \text{cm}$
- B$2\ \text{cm} \times 1\ \text{cm} \times 4\ \text{cm}$
- C$2\ \text{cm} \times 3\ \text{cm} \times 2\ \text{cm}$
- D$5\ \text{cm} \times 2\ \text{cm} \times 3\ \text{cm}$