The ore of aluminium 'bauxite' is :

Question

Accepted Answer

The ore of aluminium, known as bauxite, is primarily composed of the mineral gibbsite, which is chemically represented as $Al_2O_3 \cdot 2H_2O$. This is why Option 3 is the correct answer. Let's delve into the details to understand why this is the case and why the other options are incorrect.

1. **Explanation for Option 3 ($Al_2O_3 \cdot 2H_2O$):**
   - Bauxite is not a single mineral but a mixture of several aluminium hydroxide minerals. The most common of these is gibbsite, which has the chemical formula $Al_2O_3 \cdot 2H_2O$. This formula indicates that gibbsite is a hydrated form of aluminium oxide, containing two molecules of water for every molecule of aluminium oxide. This hydration is a key characteristic of bauxite, making Option 3 the correct choice.

2. **Why Option 1 ($Al_2O_3$) is incorrect:**
   - Option 1 represents aluminium oxide, also known as alumina. While alumina is a component of bauxite, it is not the ore itself. Bauxite is specifically a hydrated form of aluminium oxide, which means it contains water molecules. Therefore, $Al_2O_3$ alone does not accurately represent the composition of bauxite.

3. **Why Option 2 ($Al_2O_3 \cdot H_2O$) is incorrect:**
   - Option 2 represents a monohydrate form of aluminium oxide. However, the most common form of bauxite contains two water molecules per aluminium oxide molecule, as seen in gibbsite ($Al_2O_3 \cdot 2H_2O$). Thus, while this option suggests a hydrated form, it does not match the typical composition of bauxite.

4. **Why Option 4 ($Na_3AlF_6$) is incorrect:**
   - Option 4 represents cryolite, which is a different mineral altogether. Cryolite is primarily used in the aluminium extraction process as a flux in the electrolytic production of aluminium, but it is not an ore of aluminium. Therefore, it does not represent bauxite in any form.

In conclusion, the correct representation of bauxite, the primary ore of aluminium, is $Al_2O_3 \cdot 2H_2O$, making Option 3 the accurate choice.