The term "Philosopher`s wool" is an old-fashioned name for Zinc Oxide.
Option 1, Zinc bromide, is incorrect as it is simply a chemical compound of zinc and bromine and has no such nickname. It is used mainly in photographic processing in the manufacture of some types of photographic paper and textiles.
Option 2, Zinc nitrate, is also incorrect. This is another chemical compound of zinc that is commonly used as a mordant in dyeing.
Option 3, Zinc oxide, is the correct answer. It`s known as philosopher`s wool due to its fluffy, wool-like appearance when produced as a pure substance. This name is historical and not used much today.
Option 4, Zinc chloride, is incorrect. It`s a white crystalline solid that is highly soluble in water and has various industrial applications, but it is not referred to as philosopher`s wool.