This indicator has no colour in acid but turns pink in alkali. In one experiment, a petri dish containing agar was prepared with an acidic solution of this indicator. From the centre, a disc of agar $1\ \text{cm}$ in diameter was taken out to make 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 appeared and then diffused through the agar. It arrived at 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 explains these observations?
- Afacilitated diffusion of alkali solution
- Bfacilitated diffusion of the indicator
- Csimple diffusion of alkali solution
- Dsimple diffusion of the indicator