The correct option is B.
Mendeleev was the one who originated the idea of arranging elements in the periodic table according to their chemical and physical properties. He left spaces in the periodic table and predicted the discovery of those elements that had not been discovered then. One of these elements is Gallium. He predicted that gallium is going to be a metal and he gave the properties that the element will possess. He also predicted that the element gallium will be placed under aluminium in the periodic table.
Potassium sulfide, also
known as dipotassium monosulfide, consists of two potassium ions bonded to a
sulfide atom, rendering the chemical formula K2S.<span>Rarely
found in nature due to its high reactivity with water, potassium sulfide is
refined from the more common potassium sulfate (K2SO4) and is used in many
industries</span>
Phosphoric Acid - The last answer choice
I think the answer is a pure substance
