The ore that contains the metal in the form of fluoride is known as which of the following?

We are asked to identify the ore in which the metal is present as a fluoride. In other words, we need the option whose chemical composition clearly shows the presence of the fluoride ion $$\mathrm{F^-}$$ bound to a metal cation.

First, let us write the formulae of all the given ores:

• Cryolite     $$\mathrm{Na_3AlF_6}$$

• Magnetite  $$\mathrm{Fe_3O_4}$$

• Malachite  $$\mathrm{CuCO_3\!\cdot\!Cu(OH)_2}$$

• Sphalerite  $$\mathrm{ZnS}$$

Now, we inspect each formula:

• In $$\mathrm{Na_3AlF_6}$$ we clearly see the presence of six fluoride ions $$\mathrm{F^-}$$ combined with sodium and aluminium. So cryolite is a fluoride ore.

• In $$\mathrm{Fe_3O_4}$$ we only have the oxide ion $$\mathrm{O^{2-}}$$, hence magnetite is an oxide ore.

• In $$\mathrm{CuCO_3\!\cdot\!Cu(OH)_2}$$ we see carbonate $$\mathrm{CO_3^{2-}}$$ and hydroxide $$\mathrm{OH^-}$$ ions, so malachite is a basic copper carbonate, not a fluoride.

• In $$\mathrm{ZnS}$$ the anion present is sulfide $$\mathrm{S^{2-}}$$, therefore sphalerite is a sulfide ore.

Only cryolite satisfies the requirement of containing the metal in the form of a fluoride.

Hence, the correct answer is Option A.