In the extraction of \(Al\) metal from Bauxite ore, the correct sequence of various processes involved is:

1. Heating the ore to remove volatile impurities
2. Electrolysis of molten ore-mixture
3. Leaching of aluminium with concentrated \(NaOH\)
4. Grading and crushing of big ore particles
5. Mixing alumina with \(CaF_2\) or \(Na_3AlF_6\)

Choose the correct answer from the options given below:

D, C, A, E, B

The correct answer is option 3. D, C, A, E, B.

The extraction of aluminum from bauxite ore is a multi-step process that involves several stages to purify the aluminum oxide (alumina, Al₂O₃) and then extract the metal aluminum through electrolysis. Here's a detailed explanation of the process:

1. Grading and Crushing of Big Ore Particles (Step D):

Bauxite, the primary ore of aluminum, is mined from the earth in large chunks.

To prepare the bauxite for further processing, the ore is graded to separate larger particles from smaller ones. The larger particles are then crushed into smaller pieces to increase the surface area for better processing.

2. Leaching of Aluminum with Concentrated NaOH (Step C):

The crushed bauxite is then subjected to leaching using a solution of concentrated sodium hydroxide (NaOH).

Leaching involves dissolving the aluminum oxide (Al₂O₃) in the NaOH solution. This process works because aluminum oxide reacts with NaOH to form sodium aluminate (NaAlO₂), leaving behind impurities like iron oxide (Fe₂O₃) as an insoluble residue

\(\text{Al}_2\text{O}_3 (s) + 2\text{NaOH} (aq) + 3\text{H}_2\text{O} (l) \rightarrow 2\text{NaAlO}_2 (aq) + 3\text{H}_2\text{O} (l)\)

This stage separates aluminum from other impurities, and the sodium aluminate solution is then subjected to further treatment.

3. Heating the Ore to Remove Volatile Impurities (Step A):

After the leaching stage, the sodium aluminate solution undergoes heating to remove volatile impurities. This helps in purifying the alumina.

During this step, any remaining volatile compounds or water are evaporated, leaving behind pure alumina (Al₂O₃).

4. Mixing Alumina with CaF₂ or Na₃AlF₆ (Step E):

The purified alumina is then mixed with fluxing agents like CaF₂ (calcium fluoride) or Na₃AlF₆ (cryolite). 

The addition of cryolite helps in lowering the melting point of alumina from around 2000°C to about 900–1000°C, making the electrolysis process more efficient. Cryolite also helps in conducting the electric current more efficiently during electrolysis.

Calcium fluoride (CaF₂) also acts as a flux and helps in reducing the melting point of the mixture, facilitating electrolysis.

5. Electrolysis of Molten Ore-Mixture (Step B):

The final step involves the electrolysis of the molten alumina (mixed with cryolite or calcium fluoride).

The alumina is heated to its melting point in a large electrolysis cell, where an electric current is passed through the molten mixture. This process is called the Hall-Héroult process.

Electrolysis causes the aluminum ions (Al³⁺) to migrate toward the cathode, where they are reduced to solid aluminum metal (Al). At the same time, oxide ions (O²⁻) migrate to the anode, where they are oxidized to form oxygen gas (O₂).

The overall reactions at the cathode and anode are:

\(\text{At cathode}: \text{Al}^{3+} + 3e^- \rightarrow \text{Al} (s)\)

\(\text{At anode}: \text{O}^{2-} \rightarrow \text{O}_2 (g) + 4e^-\)

The aluminum metal settles at the bottom of the electrolytic cell, and the oxygen gas is released at the top.

Summary of the Correct Sequence:

Step D (Grading and crushing of ore) → Step C (Leaching of alumina with NaOH) → Step A (Heating to remove volatile impurities) → Step E (Mixing with CaF₂ or Na₃AlF₆) → Step B (Electrolysis of molten mixture).

Thus, the correct sequence is D, C, A, E, B, as the processes flow logically from one to the next in the extraction of aluminum from bauxite ore.