Chemical nature of a substance which turns yellow turmeric stain to brownish red colour is .

Give reasons for the following:

Tamarind is sour to taste.

Give reasons for the following:

We must not taste any substance without knowing about its chemical nature.

Give reasons for the following:

Lime water turns milky when we breathe through it.

Give reason for the following:

pH of pure water is $7$.

Give reason for the following:

Hydrofluoric acid is stored in teflon bottle and not in a bottle made from glass.