The titration curve of weak acid vs. strong base with phenolphthalein as indictor) is shown below. The $\mathrm{K}_{\text {phenolphthalein }}=4 \times 10^{-10}$.

Given: $\log 2=0.3$

The number of following statement/s which is/are correct about phenolphthalein is ___________

A. It can be used as an indicator for the titration of weak acid with weak base.

B. It begins to change colour at $\mathrm{pH}=8.4$

C. It is a weak organic base

D. It is colourless in acidic medium