$\begin{array}{1 1} \text{(a) Pink in acidic medium, yellow in basic medium} \\ \text{
(b) Yellow in acidic medium, pink in basic medium} \\ \text{
(c) Colourless in acidic medium, pink in basic medium} \\ \text{
(d) Pink in acidic medium, colourless in basic medium.}
\end{array} $
