An indicator is colourless in acid and pink in alkali. In one experiment, a petri dish of agar was set up with an acidic solution of this indicator. From the centre, a disc of agar measuring $1\text{ cm}$ in diameter was taken out to form a well. A white card with circular marker lines spaced $1\text{ cm}$ apart was positioned below the petri dish. $1\text{ cm}^3$ of alkali solution was added to the well in the agar and a stop-watch was started. A pink circular disc formed and diffused through the agar. It reached the first marker line after a short time, but needed longer to reach the second marker line and a very long time to reach the third marker line. What accounts for these observations?
- Afacilitated diffusion of alkali solution
- Bfacilitated diffusion of the indicator
- Csimple diffusion of alkali solution
- Dsimple diffusion of the indicator