Question

What is a philosopher’s wool?

Answer 1

Zinc oxide is an organic compound with the formula $ZnO$ . $ZnO$ is a white powder that is insoluble in water. It is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement, lubricants, paints, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, and first-aid tapes.

Complete answer:
Alchemists, as part of their rituals, would burn zinc in air and collect the residue, which formed into white woolly tufts. Since, $ZnO$ residual has a wool like texture that’s why people named it the ‘philosopher’s wool’. They called it lana philosophica in Latin, meaning philosopher's wool.
Pure $ZnO$ is a white powder, but in nature it occurs as the rare mineral zincite, which usually contains manganese and other impurities that confer a yellow to red color. Although it occurs naturally as the mineral zincite, most zinc oxide is produced synthetically.
Reaction in which Philosopher’s wool is formed is as follows:
$Zn + {H_2}O(steam)\mathop \to \limits^\vartriangle ZnO + {H_2}$
Molecular mass of $ZnO$ is $81.406{\text{ }}g/mol$ .

Note:
Philosopher's wool is an oxide of an element that belongs to the d-block. The other names of Philosopher's wool are calamine, Chinese white, the flower of zinc. The zinc oxide has a wide variety of applications, this is because of its properties like high refractive index, UV protection properties, binding antibacterial, and high thermal conductivity. It is mostly used in rubber manufacture, around $50 - 60\%$ .