When does phenolphthalein turn pink?

The correct answer is in the presence of a base.

Explanation:

Phenolphthalein is a pH indicator, which is generally colorless, however, it changes from pink to purple when encounters with the alkaline solutions. The compound phenolphthalein functions in a distinct way as it is colorless naturally, however, it turns from pink to dark pinkish color in alkaline solutions. Throughout the range of acidic pH levels, the compound stays colorless, however, it starts to turn pink at the pH of 8.2, that is, basic, and goes towards the bright purple color in stronger alkalines.

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.