The chemical formula of cryolite is :

Question

Accepted Answer

Cryolite is a mineral that is primarily composed of sodium, aluminum, and fluorine. Its chemical formula is Na$_3$AlF$_6$, which corresponds to Option 2. This formula indicates that cryolite consists of three sodium (Na) atoms, one aluminum (Al) atom, and six fluorine (F) atoms. Cryolite is often used in the aluminum industry as a flux to lower the melting point of alumina during the electrolytic production of aluminum.

Now, let's examine why the other options are incorrect:

1. **Option 1: Al$_2$O$_3$ . 2H$_2$O** - This formula represents hydrated aluminum oxide, also known as aluminum hydroxide or bauxite in its mineral form. It is not related to cryolite, as it lacks sodium and fluorine, which are essential components of cryolite.

2. **Option 3: Na$_2$AlF$_6$** - This formula is incorrect for cryolite because it suggests a different stoichiometry, with only two sodium atoms instead of three. The correct formula for cryolite is Na$_3$AlF$_6$, which maintains the proper balance of sodium, aluminum, and fluorine atoms.

3. **Option 4: NaAlF$_3$** - This formula represents sodium aluminum fluoride, which is a different compound from cryolite. While it contains the same elements, the stoichiometry is different, with only one sodium atom and three fluorine atoms. This does not match the composition of cryolite, which requires three sodium atoms and six fluorine atoms.

In conclusion, Option 2 (Na$_3$AlF$_6$) is the correct chemical formula for cryolite, as it accurately reflects the composition of the mineral with the appropriate number of sodium, aluminum, and fluorine atoms.